Agree with Solteris.
I'm loathe to give pickup advice to a 15 year old. But I'm a lot older than you and got into game late, so I may be biased. You need to be focussing on things besides girls at your age: having fun without girls, sports, hobbies, music, reading or whatever. Developing your personality in other ways will make you much more effective in pickup later, happier and less one-dimensional.
Don't become a total pua obsessed nerd and end up becoming like a lot of other fuckwits on this board. There's time for that later
My advice to you would be to find girls around activities and hobbies you are interested in and grow things from there. Keep it simple. Don't overthink it. Find a girl you like. Get friendly with her. Bust a move and then try to sleep with her. This is a time when you want to be having short or long term girlfriends rather than trying to 'pick up'. Also be as social with other guys, kids in school. Get out of your comfort zone and make as many friends as you can. Don't ignore other stuff - school work, hobbies, sport etc. as being a total social butterfly is highly overrated.