It's also a good idea to turn the wheels all the way in each direction and check for other clearances, as well.

If you have 15x5.5 now with a 38 offset and you went with a 15x6 with the same offset, you would lose 1/4" of that clearance (1/2 of the added wheel width). If clearance becomes an issue, moving the offset outward will add to the clearance.

Don't forget to consider fender clearance if you start getting WIDE and pushing the offset out, though!