[hewittca]

The concern with using drop blocks and smaller diameter wheels is the scrub line. As in, if the tire were to essentially come off the rim, what would touch the ground first? You want it to be the rim and not any fixed part of your suspension. With smaller diameter wheels, you run the risk of the u-bolts being the first point of contact with the ground, not your rim. That would be a rough ride! What you can do is measure your current u-bolt to ground and rim to ground distances. Whatever the difference is between those two (where your u-bolt to ground should be the larger of the two), that is the absolute maximum block height you could use. If it's less than two inches, you definitely don't want to use 2" blocks. All that said, I think there are quite a few guys running 2" blocks on 15" rims, so you should be ok. It is good to check though.