Do you have money? I mean, you're 15 year old. If you want to be able to charge people for your services, you'll have to have some decent equipment.
When I was 14 I started to buy stuff. I had money because I lived with my parents and was working each weekend with Sound Companies. I invested all my little dollars in equipment. But I couldn't really charge people untill I got serious equipment. Now with charge I mean a reasonable fee.
I would suggest you buy the stuff you'll think you need, but take it slow. Try to work
with people instead of seeing them as costumers. Age could be a little problem. I personally would not take a 15 year old serious because of the simple fact that he can't have any major experience with recording and productions processes. I don't mean recording the keys at home, but real life bands etc. It takes knowledge and most of all experience.
I myself have been able to setup a commercial studio that is up and running stable. The only way I could achief this was by
1. pure luck (right people, right time, right place)
2. being so determinded that is was annoying
3. keeping investing all the time.
4. a little bit of talent (ahum ahum)
If you try to get a loan and invest a lot at once, I don't give you a real change. I think the equipment would be outdated before anybody took you serious. invest slowly but constantly would be my advice. That's the way I did it, and I started at your age. I worked for me.
At your age I would try to get as much of experience as one can. Your 15, your mother still makes your sandwiches

D ) Profit from that. Once you'll have to able to make it on your own, you have no time to get a lot of experience anymore. you'll have to sit in an office like from 9 till 5 like all the other losers at this forum

D

) instead of recording the whole day like me

cool: )
See, I'm still annoying
Go and roady with a sound rental company. Good mixers are hard to find, but you will have to proof yourself to be the right man for the job. No one is going to hire a 15 year old they don't know that comes in and says
I want to be your new FOH dude If you manage to get on the road with them, and ask to do the soundcheck you'll get noticed when your up to the job. This is also a great way to meet bands and people. Mayby if you see a band, you can ask them if they want to record a demo with you for free. That's lots of experience for yourself, and imagine the benefits if you do a fantastic job. You'll name will get around, I assure you.
Now come back after a few years and tell us how it went (

)