There are many jobs you could apply for at the age of 15 years old. It usually depends on your intrests. If you are an active person involved in sports, you could help coach, or if you enjoy reading, there’s always the public library. But, if you still dont know, theres the local grocery store, clothing outlet or music stores. Many malls have lots of places, and you dont need to go far for your lunch break : Food court. You could also work at a restauraunt, as a waiter/waitress, dishwasher, or greeter.
I hope this answer is helpful, and enjoy your job search! 🙂