I'm still running my 32x11.50 BFG ATs.
15mm = .6" I got some rubbing on the front bumper wing but that was because my bumper was pushed back about 3/4" from nosing into a berm. I adjusted it and no prob. The only place I am slightly concerned about now is the rear where the tires were about 1/2" narrow enough to stuff at the point where the wheel opening arcs under the rear door. The extra .6" outwards will make it close.
I'll see if I can flex it out sometime soon. It's been raining out here and I'm not game to go get muddy for nothing at this point, I just cleaned all the mud from under my X last week.
Brent