You shouldn't have to drop the diff with a 1.5" lift.... heck you really don't even need to drop the diff with a 3" lift. I've had a 3" lift on my VX for the past three or four years and finally tore the drivers side boot last year and only because they where ten years old and had dryed out. I was told that if I got under there and "treated" the boots (ArmorAll, or some such thing) every now and then they probably would have lasted longer.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless