Daytime temp of 15F, I'd go with the R1, which is also great for sleeping in. My new R1 hoody was a perfect match for 15F when paired with an OR Ferrosi hoody. Can't say I've ever been more comfortable when hiking.
At 0 to -10F, if you sleep warm and are wearing down layers under a 10F quilt, I doubt the baselayer's going to matter much.
I have several 200wt Icebreaker tops that make great sleepwear when brought for that purpose, but don't think much of merino for active wear.