How do, i've got 4x4 cossy calipers on my 98' escort and normal have then tucked nicely behind 17" compo's.

My question is what offset would i need to get a set of 15" back on as the RS2000 standards wont clear the calipers. dont really want to whack on 5mm+ spacers on. I have about 10 newish tyres for the 15's and want to use them up - which normally doesn't take to long ; )

any and all help appreciated