I think your main problem here will be lack of any qualifications for IT work. It is the same for everyone not just a 15 year old, also they want people,to be able to work weekdays when you would be at school. Most offices will use agencies for any temp work. Sorry to put a downer on things but unfortunately that's the way things are at present. Hope you do find a job of some kind so you can get your pc upgrades though.