I thought the same thing when I started out (at your age, too). My friend and I played together for a few months, and then we met another guitar player and drummer who were just starting out. Gigs started and just kept coming. Once you reach critical mass, opportunities to play in front of people tend to present themselves, and you could very well end up gigging much more quickly than in a year or two.
All of the gear being recommended so far will serve you well. If you buy an amp intended for bedroom practice only (or for playing at low volumes with one other person) you absolutely will end up replacing it once you start playing in a full-blown band. Not saying you should buy something bigger at this point; just be prepared to do so if you progress further.
Beyond that, a few pieces of advice:
- Work with an instructor to help get you started. In hindsight, this is the most important thing I would have done differently and it would have made a big difference in how fast I progressed.
- Play a bunch of different basses and alway always always buy the one the feels best to you.
- Protect your hearing. That muffled ringing noise you hear after playing with a loud band is the sound of your hearing going away. It may not seem like a big deal at 15, but it absolutely will be at 50. Keep the volume down or use ear protection.
Welcome to Talkbass. (Where the beauty of the basses is exceeded only by the people who play them. Or maybe it's the other way around.

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