You're 15...what an excellent age to start video editing!
At your age, I'm assuming you've grown up with computers? 90% of learning an NLE is knowing your way around a computer. The other 10% is learning the software, IMO.
A couple of cheap ways to get in the door...as Frenchlemon pointed out, buy a camera...assume you have a computer, so pick up some software. If you can swing it, Final Cut Express or Adobe Premier Elements. Both of these programs are excellent starting points to learn their bigger brothers...or eventually, move in to a full fledged AVID studio.
Drop $25 at Lynda.com and learn the software. MacPro Video and Creative Cow are also excellent resources.
As others have said...find out if you dig it first. By the time you graduate high school, you'll be an FCP/Premier Master

IF you spend the time and energy to learn the software AND the fundamentals of story telling with video editing.
That's how I pay my mortgage...our car payments, and feed the family

My wife and I own a video/audio production company and I LOVE going to work. But, as others have mentioned, working/owning your business is a LOT of work...If you can pick up some skills learning on your own, drop an ad on Craigslist to freelance yourself.
There is NO substitute for experience. Whether you're behind the camera, in the editing suite, or dealing with clients....the more you do, the faster and more efficient you'll become. You'll also figure out exactly what it is you want to do...or pursue in college.
That's another point...and one I differ on than others. College degrees are paramount in this day and age. I'm not sure I'd pursue a Liberal Arts or "Film/Drama/Pub Com" degree...but ymmv. You can always minor in production and Major in a degree in demand.
If you do what you love, you'll enjoy life. It's not always about getting rich, but more about living comfortably and enjoying going to work each day.
Good Luck!
Jer