how to earn lots of money at 15?

Here's an idea off the top of my head: use your computer skills to build a website (or make flyers) to let the people in your area know that you are available to do odd jobs.

When I was 15 I did odd jobs around the neighborhood (we lived around a bunch of old folks) like mowing, cleaning gutters, hanging X-mas lights, etc. I had a deal with my dad to wash and detail his car for $50 once a month. After I had a few bucks in my pocket, I bought a little sign that I put out on the sidewalk wherever I was doing the odd job, while I was working and then took it with me when I left. I also had cards printed up (you can get them free of charge now at a lot of places on the net) that made light of the fact that I was a teenager looking to do some work.

"Tired of yelling at your husband to finish the Honey-do list? Call me! I'm a teenager who will do odd jobs for just $10 an hour!"

It worked. I paid cash for my first car. And second car. And college. And I now own a gold and silver bullion business.

The trick to making money (at any age and in any economy) is deceptively simple: Ask for it, then deliver.

Change your name to Justin Bieber and sing really annoying stupid songs.

Pimp yourself out.