Your boss will be paying $15 an hour to people who's contribution to the workplace doesn't equal that much, at least while they learn how to hold a job. You can ask, but he doesn't have a pot of money laying around, and he can't just pull it outta his a__. He simply won't have the extra money to give you. Your new colleagues will earn as much as you, without contributing nearly as much to the workplace. They will be getting the money that would have been your raise.