Well no one can say that beyond 1.5" of drop the shocks will blow. It's not like 1.6" is going to be playing with fire.
Just bring it down to where you like it, see how it rides. If you keep one or two finger gap (yeah, finger gap method is pretty arbitrary, but you get the idea) and that should be fine. Sure, if you slam it 4 inches and are tucking tire, it's going to put a lot of stress on the shocks, but the difference between 1.5 or 2.0 inches is pretty minimal. It will depend more on how stiff the springs are, what kind of roads you drive, how you drive, etc.