If four guys smoke 1 blunt with 1.5grams of weed how many hits should each one take?

1.5 grams is quite a lot. 5 hits (relatively small ones) should make you feel it, after 8-9 you'd start noticing some changes. The best advice I can give is to just feel your way through it. With a blunt that size you shouldn't hesitate to just put out the roach, and if you so wish, rather light it up again after a bag of funions.

Good luck.