Bringing this one back from the dead. For the rear, 15x9s (at least for Advanti Storm S1s, but I imagine generally true for all the options) need to be spaced out to about a +20 effective offset to clear the lower control arm. You might be able to get away with a few millimeters less, but run the suspension through the entire travel range to confirm. +25 offset would rub even at full droop, and as the suspension compresses, the control arm gets even closer to the wheel. +22 offset clears at full droop, but might not through the entire travel range. The lower control arm is the main challenge to running 15s in the rear, so you can work backwards from the 15x9 needs +20 rule of thumb to figure out clearance for other widths.
2011 Lotus Elise SC Final Edition 15 of 15 - Ardent Red