I think the simple answer to the question of why a man would prefer the sexual activity of a 15 year old boy is that the man longs to be a 15 year old boy again. The reason why a man would long to be a 15 year old boy again is a 15 year old boy has no responsibilities like having to work at a job, help with kids and housework or meet the sexual needs of his wife.
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver
