I'm 15 as well, and I think I have the same type of asthma as your son! I think the doctor just called it "Coughing Asthma". I really don't know, I was 2 at the time. Lol But anyway, now I'm about
65", so apparently my "green zone" would be about
440. Lately I've been about
260 though. So in my opinion, your son's doing very well... But what do I know!
He should be fine though. If he seems all right to you, I think he's doing really great!