He sounds normal to me! Not sure when they start following you around - mine never did that very well! But it's all based on your expectations and how well those are communicated to them. Every kid is different, but I'd say there's no way a 17 month old is going to follow directions like that unless they are quite shy or nervous and clingy. Then they follow you in stores but won't let you leave them with a sitter or preschool!
15 words sounds right. Remember that he's developing skills in some areas and not spending as much time on others. So if he's curious, that's great. If he's not as verbal, that's probably not a problem. One thing that happens is that we moms are SO GOOD at understanding their baby talk or their body language that they never really HAVE to talk. Mine was a non-verbal 16 month old who just grunted when he wanted something - until I said, "Listen, whatever it is in this world that you want, you can have it, if you just say the word and stop that infernal whining." (I know, dumb me, he could have asked for a car!) Anyway, the kid looked right at me and said "COOKIE" and he hasn't shut up since. But instead of talking, he was very active, inquisitive, athletic, coordinated, and more.
As you go along, you may find that he can learn that it's okay to explore in area A but not in area B, or that if he stays with you in Target then you will take him to the playground where he can run around. But he's not there yet. I wish there were rules, but there aren't. Every kid is different - which is why we're all on Mamapedia looking for help! LOL.
What you're going through right now is frustrating but good practice for when he's a pre-teen and won't talk to you or stay with you in a store!