A buddy got a complete Carbon 15 3+ years ago and it's worked well. For him. Personally I'd rather have a standard 7075T6 lower myself.
I wouldn't put a heavy upper on it since it's designed for the lightweight C15 M4 upper.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek