Best 15 Degree Sleeping Bag in my opinion, and here's why!
I have been a backpacker over 25+ years. I finally decided to purchase THE BEST 3 season sleeping bag on the market, bar none. After reading numerous articles and reviews, I narrowed it down to 3 finalists: Montbell UL Super Spiral Down Hugger #1, Marmot Helium 15, and the Mountain Hardwear Phantom 15.
Being a Backpacker Magazine subscriber for over 5 years(Excellent magazine) I was leaning towards the Marmot which has won the Backpacker Magazine Editor's Award. But then I found an excellent website which changed my mind: www.outdoorgearlab.com. It showed some of the most detailed reviews I've ever seen, and they are absolutely correct! Marmot has no neck baffle, which does not insulate the body from the cold air coming into the body area from the face opening. Also it has an unusually wide torso area which is good if you are a big stocky guy, but otherwise it is inefficient if you have athletic slender or medium sized body (I am 5'11" 155Lbs). Montbell is also excellent bag, but the hood design is pretty poor and I really dont' care about their stretching ability. It also adds few more ounces.
Finally there is one more bag out there, the most expensive Marmot Plasma 15 which costs $470, but it's way out of my price range.
So there it is, my final verdict is MH Phantom 15. And I love this bag! Backpacker Magazine just proved that they are not always right! :)