Yeah, there will be an adjustment. He's going to be playing night in and night out against quicker players - older players, and he will adjust as he progresses through his four years. He'll learn to adapt - even if he is slower.
I remember watching Dough McDermott in High School w/ Harrison Barnes (lived in Iowa at the time) and thinking he might be too slow to ever do much in college...not comparing the two (but both are playing for their father), but players learn to adapt and if the handle is good enough, or develops enough to deal with shedding quicker defenders, they can usually figure a way to get open/shots.
BB has a chance to be really good with that shot - but if he wants to be great he has to figure the other stuff out. Worst case scenario is we end up with a sweet shooting slow dude for 2 or 3 years (assuming this year his role is limited).