Rims will probably interfere with the outer end of the upper control arm. On a 15x7, 4.5" BS is about the limit there with a stock style rim shape. Might get a little more or less with a different rim cross section, but not alot.

As far as tire width, it depends a bit on construction. Some 235s will be OK on a 7" rim, but its not ideal. Check with the tire manufacture's recommended specs.

Edit: agree that the aspect ratio will make a difference. a taller aspect ratio will allow wider tire to fit as others have stated. Whether it puts more effective tread on the ground can be very tire specific.