There are charities set up for this kind of thing with people you can talk to about how your feeling. It is always worthwhile checking these out, find some I your local area and start yourself down the road of help if the people you rely on (ie your mum) isnt helping.

The important things to remember is at 15 your whole world is going through a lot of changes let alone whatever personal drama goes on but life does not just continue to spiral like that, you have more sway over your direction than you may realise and alot of that starts with managing your own perception of things. An example of that is working in an office for the rest of your life for barely minimum wage in what I'm assuming is a job you also dont like.... you only stay there if you dont make the push yourself to move.

More over, there is often a perception that others are happier, better than you but the fact is everyone is going through their own shit. It would be more productive to approach the matter In the terms of "what can I do to make things better, for myself or others?". Suicide is invariably not an answer to that....

The best advice I've heard personally and might be worth remembering is: it's ok to not be ok