He went on to college and then to
grad school and has a PhD from Yale. 15 months is also a little on the early side, but personally, I'd just keep a track of it, address everything with the pediatrician, and stay on top of it, and try not to worry too much. Plus if you stress out, your son might pick up on it and feel undo pressure to perform (i.e. speak). Oh, and terrible twos start around 15 to 18 months, so maybe he's just starting a little early with the tantrums.