1st things first..
Hello Dangerous, and Happy New Year!
2nd... I am not a parent, but here is my 2Ę
Where do 15 year olds get liquor... where do they get drugs?
Where there is a will, there is a way.
He may have a friend who gave it/them to him or her.
I think if they are old enough to go through the motions, they should be old enough for the protections.
I know that it not a sure thing of protection against STDs or pregnancies, but an ounce of prevention.....
Maybe a step beyond the talk would be in order.
Show him, or introduce him to a teen parent who is going through what will happen, and what will/should be expected of him if it happens.