I wondered about my now 6.5 year old at about the same age. He wasn't much of a talker until like 2, and then he started talking little by little. He's now a perfectly healthy, perfectly normal, sometimes even over-talkative first grader.

As for his not liking to sit still to read a book and stuff, that sounds totally normal too! He's very young, and at that age, my kids wanted to learn by doing. They learned through getting up and moving, running, climbing, staying busy.

Having said all that, because your doctor suggested early intervention, it might be a good idea just to have him assessed. That way, you never have to worry about "should I have done that, back when he was 1.5"