We don't allow 15 year olds to sell alcohol, why would we allow them to sell sex? I'm sure one doesn't have to stretch far to find other examples of professions we don't generally let 15 year olds engage in - you don't seriously think a 15 year old cop with a gun is okay, do you? Or a 15 year old soldier on the front lines? Are you okay with a 15 year old doing your next heart surgery?

This is clearly a situation that society knows how to handle via a fairly wide variety of methods and control systems.