Factory Wheels and Spacers ?

Crooz

I've searched the forum several times now trying to determine the following, I had no luck.

If I add 15mm 'Bolt On' spacers to the REAR (the spacers that already have lugs, and you bolt them over current factory lugs) will the factory lugs protrude beyond the spacers and interfer by hitting the wheels when you attempt to remount them?
.... or do the factory Rear wheels have an inset (space) that allows such a protrusions to not contact the wheels? I have found that the Front rims won't accept these type of 15mm (and many mfg website note such for the front wheels) but how about the REAR's?

I really don't care to get into changing out the rear factory studs, so, if the 15mm noted above won't fit on the rear to protruding studs, will 20mm bolt on's work? Are they thick enought to solve the problem?

Thanks in advance for your answers.