I don't know for sure but that seems excessive. 15"x8" rims were on my truck when I got it. I have no idea what the backspace was but it seems like they rubbed somewhere in there during lock to lock turns.
They were also too wide to steer easily with stock components and no power steering.
My current rims are 16"x6" with 3.5" backspace. They don't rub or anything but if I were ordering them again, I'd order 5" width.
