op it was about a year. it literally was very intense for a while and then he dumped her. she cried for a few days, bloody awful, and then was fine.
her dss strangely enough were very angry that he dumped her even though they had always hated him!
you are doing everything you can. 15 is a young woman and you are right to let her fly a bit. what else can you do really?
as I said keep talking to her, keep telling her how to keep herself safe and to respect herself, talk about contraception because let's face it the biggest disaster would be an unwanted pregnancy.
I know most of my dds friends have had sex. she's told me. I have airways been honest and told her that when she feels the time is right we will go to the docs together and chat about contraception.
my one proviso with your situation would be any sign of violence it controlling if your dd is absolutely a no no. but sure you would step in then.
for the rest let it run it's course. oh GCSEs soon so that's a good opportunity to chat to them both about more time spent studying. dd has a lovely bf now and we have a Rota of seeing each other in the week to leave time for study and homework.
your ds is a lovely lad to worry like this mine were the same and more so as dh works away so they felt more responsible. sometimes I had to remind older ds that yes his views are valid but actually i an in charge here 
sure it will all pan out. but wasn't it much easier when they were babies??? 