Off-Road "Baja Boxster" Wheel Question

[BajaBoxster]

Hello All,

I hope all is well. Let me just start off by saying the 986 forum has been extremely helpful in my Boxster escapades so far, but I need the help of the community for a unique build.

We recently bought the cheapest 986 in our area with plans to turn it into an off-road "trail" rig to take to the 2017 Easter Jeep Safari. The plan is to run all 149 miles of the white rim trail in our '99 2.5. The first major mod (besides a suspension lift) are a set of A/T tires. I really would like to run a 205/75 Grabber at2, but that would require a 15 in rim.

Would a 15 inch work on a non S front and rear, or would I have to step up to a 16?

Thanks all for your help in advance!