Go around your town centre and bring a bunch of CV's, apply anywhere you can.
Mcdonalds is good for young people, it may not be glamourous, but the pay isnt too bad and they will work around you for times.
Some places will hire 15 year olds, just have to find out where. Could work in pub kitchens or I was even going to get a job in a cattery, random places like that will be happy to hire you....of course there's always newspaper rounds.. And if you're 16, mcdonalds will hire anyone and some money is better than non at all