I suspect the 15-degree rating is pretty optimistic on the Eureka bag. Most synthetic bags rated at 15 degrees would weigh a pound or so more.

Speaking of Eureka, though, a friend of mine just bought a Eureka Spitfire 1 (1-person) tent somewhere on line for $79. He likes it so far, and I'm starting to want one. I think they're $99 at Campmor.