I had my 235's and 31x10.5's on 15x7's
Had to get wider rims to properly run 12.5" tires though - 7" will cause 'crowning' at good pressure and potential lower tire life if running at lower pressure to flatten the tread.
15x8 is the standby for 12.5" tires. General rule is not more than 4" difference.
If you decided to future proof yourself, you can run 235's on 8" rims and they will look wide, but you would not want to air down below 15psi or risk slipping a bead. Your 31x10.5" tires will also mount well on 8" rims with similar watchouts for low pressure. I generally only deflate to 15psi anyways due to an under powered air compressor, but do just fine.
'00 XJ - Somewhat modified
'01 Venture - high mileage, paid for, shut it