Even a 8150 shouldn't be running that bad on LOW not with a 7950 , My GF has a 1090T (stock) with a 7950 and gets 60fps+ constantly in multiplayer maxed out settings at 1080p, and a 8150 is not that *** compared to an X6 1090T, so thats not your problem
something else is going on here
We need more details, what motherboard, ram , PSU
what AMD GPU drivers are you running
what res and settings are you playing BF3 at