Oh, but he did help your son. First off, being convicted of 15 over results in automatic license suspension by the DMV for 30 days. Next, the DA will likely only deal you down one level. The levels as 0-9 over, 10-14 over, and 15+ 0 over. So by dropping you sons speed to 10 over he will plead down in court to 9 over and the net result will be no insurance increase provided you don't get another ticket within 3 years. Don't waste a PJC on this (provided it gets dealt to 9 over,) save it for the next ticket. If he is on your insurance policy, if anyone else on the policy has a ticket this could change the need for a PJC.
Not a lawyer, this isn't legal advice, been to traffic court in NC a lot.
I got saved by a trooper like this once, he reduced my speed of 95 in a 55 (yeah, I was young and stupid, he actually asked where the fire was when he jumped out of his car) to 83 in a 55. The DA in Wake County generously offered 80 in a 55, I asked what good that would do and counter-offered 79 in a 55. She agreed, and shuffled me off to the magistrate (they do things differently in Wake County, in my home county you still see the judge.) The magistrate immediately offered me a PJC (I didn't even know what one was) of his own free volition and I jumped on it (sounded like a good deal, no fine, don't get a ticket for 12 months and your insurance doesn't go up.)
