1.5" can be and should be enough, but when I have less wood to work with, I try to "find" wood I can use in the stave...bendy handle, or smaller handle with more abrupt fades, shorter arrow pass area, and try to relieve stress on the bending-but-stiff-but-narrow areas.
But, let me suggest you slow down on your tillering. Never pull the bow more than the final draw weight during tillering, and get everything as good as your eye can see it before you go on. Get a crayon or pencil and mark all the areas that need to bend more. I have gone so far as to wrap masking tape over areas I knew I shouldn't touch.