Forget the Offset dimension, it's not a useful measurement for Jeeps.
For a 32x11.50, you can use more backspacing like 4" so the wheels won't stick out as far. Personally I'd rather go with 4.5" if available, I don't like the wheels sticking out any further than absolutely necessary.
And how much more the wheel will stick out depends on the width and backspacing of your current wheels.
Assuming your factory wheels are 15x7 with the usual 5.5" of backspacing, the outer edge of a 15x8 wheel with 4.5" of backspacing will be be positioned 2" further out.