This sleeping bag kept me warm for three nights, the first night got down to 42 degrees Fahrenheit (5.5 degrees celsius), and the second two nights it got down to 39 degrees Fahrenheit (3.8 degrees celsius). All I was wearing was thin nylon hiking pants (the kind with zippers to turn the pants into shorts), and a T-shirt. I am five foot, eight inches tall and weigh 180 pounds, and I was super comfortable inside this "mummy bag". I think if you are five foot, ten inches tall you would still fit, but taller than that, and I would recommend you get a longer version. The "hand" (or texture) of the outside and inside fabric felt very "plastic-y" to me, but apparently the fabric breaths well, as I did not get that "wet" in ten minutes sweatiness feeling like I get when I put on my rain gear, so I very quickly grew to like the "hand" (texture) of the fabric. The zipper is big, and the inch wide protective zipper flap makes sure you don't snag the inside fabric as you zip it closed. There is a velcro fixture at the top by your head, which allows you to have the hood secured over your head, but leave the zipper opened up a foot or so, so that you can put one arm outside the bag in a flash. That helped me keep from feeling too claustrophobic, so I really liked that feature. I got this sleeping bag, because I had tried "quilts", but every time I tossed and turned turn the night, a whoosh of cold air would come in and wake me up. I understand the idea behind quilts (why carry the extra weight of the down underneath you, when it is not going to insulate you from the cold all squished flat by your body weight), but since the quilts don't wrap all the way around you...for me anyway....they are way too drafty. The foot of the sleeping bag got a little bit wet each night, from the condensation on the inside of the tent...not the bag's fault...anyway, each day durning a lunch break, I would hang the sleeping bag on a tree branch in the sun, and by the time lunch was done, the wet foot part of the sleeping bag was all dry again.

UPDATE after 3 straight weeks of backpacking and having this for a while:
This sleeping bag packs down super small and is incredibly light! I really love that about this sleeping bag and am very impressed! It's also really soft and silky, so it feels nice, too! It is mostly warm because the front of the bag puffs up a lot, but the back half and hood of the bag are not that warm and are pretty thin. I slept in it at temperatures down to 30F and I could have been okay if it were a little big colder, but I'm not sure about 15 degrees... The zippers are okay. The smaller zippers aren't great, but the main zipper is pretty good. It's also a tight fit, which helps keep you warm, but I move around a lot in my sleep and felt pretty restricted. This is actually an amazing bag for the price and I would get it again (probably the bigger size this time) but I can understand why some of these things might be a no go for someone.

ORIGINAL post:
After having slept in this bag for a couple nights, here are my impressions:

Pros:
-I plan on using this sleeping bag during my three weeks on the JMT and I am very happy with how lightweight and small it packs down. I am very accustomed to using all my weight to cram my sleeping bag into the lower pocket of my Osprey bag, but this sleeping bag swims in that pocket!
-It's very easy to cram the sleeping bag into its stuff sack
-The material feels really soft and silky, and the bag fluffs up very nicely. I haven't had a down sleeping bag before, so I cannot comment on how it compares in that sense.
-One of the awesome features for me is that you can unzip the sleeping bag from the bottom. I like to stick a leg out of my blankets when I sleep and this feature allowed to regulate my temperature really well if it's a warm night.
-I'm a 5'5" woman and I fit pretty well into the regular-size bag and stayed very warm when I camped in 45F nights.

Cons:
-I wish the bag had a little more space, particularly around my legs. I move around a lot when I sleep and I felt a little too constrained by the bag.
-I stayed mostly warm at night at 45F, but I'm not sure I would be warm at temperatures much colder than 40F. One reason is that my blow up pillow (while small) takes up the entire hood of the sleeping bag. It would be pretty difficult to cinch the hood around my head if it got very cold. Another reason is that I'm usually sleep on my side and the back portion of the bag is fairly thin.
-The zippers are okay, but I will probably add zipper ties to some of the zippers so I can grab them more easily.

Overall, I think this sleeping bag is well worth the price and I would recommend it, but there are a few caveats you should be aware of before you buy.

This bag is toasty! As with any piece of gear, I did an immense amount of research about it. I wanted something warm and light with great compression that wouldn't break the bank. A tall order for a mummy sleeping bag, I know. Well, all of my research paid off. I ALMOST purchased the 0 degree version of this bag and am so glad that I didn't. I'm generally a warm sleeper and anything more than this bag would have been too much. I used it in northern Europe during the mid/late fall and found myself unzipping it in the middle of the night because I got too hot. Sleeping on my side proposed no issues and I am yet to have a single feather poke through.

We experienced a lot of rain so it did get wet one night but the fabric repelled the water like a champ. The zippers are high quality YKK but with how thin the material is, they will zip right over it if you're not paying attention. This isn't an issue after the first time it happens though because with a little awareness you're not likely to do it again.

I don't think that the compressed picture really does the bag justice. This thing compresses A LOT with the included compression sack. What's really noteworthy though, is that more compression would be possible with a different sack. The included sack has its clips sewn on with not enough room for it to be compressed 100%. I was able to fit this comfortably in the bottom of my bag next to(not beneath) a pair of shoes.
The weight is good as well. According to my scale it came in at 2.53 pounds which is a hair less than advertised.

My only wish is that it came in some better colors. I've never been a big fan of orange.

Finally, the most important thing to me is that the down feathers are responsibly sourced by being a byproduct of the meat and egg industry. This was a major concern as many bags are made in China so I was relieved to see that they use humane down.

The quality of this bag completely surprised me. I thought I was taking a big chance on a budget friendly down sleeping bag. I've used several big brand down bags and this Hyke and Byke Eolus 15° bag compares to some of those.

I've used this bag at least 10 times in the couple weeks I've owned it and in temps as low as 23°f and the bag has performed excellently. In fact I've had to open the bags to vent the heat several times in cold weather. I do sleep very warm and I do use a cheap Ozark trail liner.

I got this bag because of the weight, the cost and the materials. 800 fp goose down just screams warmth to me but I'm used to seeing any bag with that fill costing over $300 and I didn't completely trust that I'd be happy with this purchase. It really does keep me warm. Extremely warm. I've noticed some folks saying the bag reminds then if being in a trash bag (black/Clementine) and I get it but it's far from a trash bag.

I'm a big fan of the long baffles as they seem to spread out the warmth well. They company told me the top half of the bag is stuffed at 60% whereas the underside is stuffed at 40% which I'm very happy about because down doesn't insulated well when compressed. *Be sure to fluff up the bag when you get it and when storing it long term either hang out or put it in a large mesh/breathable bag.*

Now the down is not treated. That's something you have to do yourself but the company recommends that you use a down cleaning service to treat your bag. Reason being is that the warranty does not cover you if you mess it up in the cleaning process. The outside of the bag is treated with dwr which is good for most situations unless your climate is very wet. I do plan on getting my bag treated. The zipper.... Is not snag free. It tries and unsnags relatively easy tho. It's a decent zipper.

Something I'd like to recommend is the cut of the zipper at the top of the bag. If you look at big agnes' bags the top part of the zipper (up at the shoulders) comes in and makes easier to zip up at the top. I don't think this would cost much extra to do but would be a great addition to this already great bag.

All in all this bag, for the cost, is absolutely amazing. You can see where corners have been cut to provide a low cost but if you need a good quality bag to get you through this Eolus will do it just fine and some. If you're going to be spending most of your time in the backcountry I would highly suggest you get this bag treated or just get a higher quality bag. If you are looking for a bag that's lightweight, packable, warm and budget friendly this is a very good option. You'd be very hard pressed to find an 800 fill power goose down bag that's this lightweight at this quality and cost. Plus it's nice to support a small company that's trying to help people afford gear and gets us outdoors. I'll be taking this bag on the Appalachian trail for a winter section hike and I'll be sure to update this review during/after I've really put it through the ringer.

First I must say, after reading some reviews, there are some caveats that should be assumed before using this or any sleeping bag in cold weather. First, you must use an insulated sleeping pad. On the bottom of the bag, the down will crush under your body weight drastically reducing its insulation factor. Second, the temperature rating of most bags is a survival rating, not a comfort rating. A 15-degree bag will keep you from hypothermia down to about15 degrees, but you will not be comfortable. Generally speaking, assume double the survival rating for comfort rating 15/30. Knowing this plan for insulated underwear, snowcap etc. to increase comfort. Lastly, use the neck drawstring. if you are approaching lower temp limits the neck drawstring is vital. Leaving it untightened, provides a huge air gap around for the heat to escape. The insulation will only do so much, you must ensure all the holes are plugged.

For this bag, I have to say it was well worth the money. I use a down quilt, personally, but needed something for my 10-year-old daughter during our hike into the Wind River range of WY. Since you are never below 8000 feet in altitude the temperature swings are drastic. 70-80F during the day and 10-30F at night. She used the 15F bag in a short length, along with insulated underwear and a Klymit insulated V Pad, and she was comfortable every night. My only complaints about this bag are the weight and her bag had down the neck draw sting sleeve which leaked out. The leaking down wasn't an issue, because the neck drawstring sleeve is separate from the main bag baffles, but the whole time I was inspecting her bag thinking it was ripped somewhere.