Personally, I think it is not appropriate for a 15 year old to be in a university, basically because they are too young to undergo such exposure. They are too young to take responsibility for themselves especially since they don't have their parents with them. But there are still adults that still go wayward.
So what matters is how disciplined he is, his ability to withstand any type of pressure that will make him go astray.
Fifteen years is enough for the parents to inculcate good morals in a child.
But following the laws, a minor is still a minor