I've just switched to 17'' rims and 37'' BFG Mud Terrains! From 38'' boggers and 16'' beadlocks.
I've got 17'' rims on my dually pickup. Looking at going to 19.5'' soon.
My wife's car even has 16'' rims.
I think 15'' are going the way of the 16.5 rims, slowly.