I'm sorry friend but you're not going to make that, especially not at age 15. On the bright side though, it's definitely not a once in a lifetime experience. Later when you get older, money will be easier to get, and of course much more flexible with time. Being hired will be a lot more common and you'll start at a (probably) 7 USD per hour payflow at age 16 if you do decide to start working. This amount can vary, but if you're not selling yourself short, that's the salary you should root for.
It's common for people of your age to think that everything that happens is very important and will never happen again, but life is a lot longer than you think, you'll definitely have a chance to go to Japan again, maybe with your brothers, maybe with your friends, but for sure at an older age.
I was the same at your age, when I was 16 years old I just had to get a ticket to PA to visit someone, and if I didn't that would mean the end of the world to me, I eventually got a job at a local fast food chain and tried really hard at it, but despite that it killed my free time and my mood because I wanted to raise money so badly.
After a few months I had only raised about 20% of my goal and I couldn't bear the job anymore, so I quit.
It was disappointing to accept that I couldn't go on said trip and that I wouldn't see that person, but at that age, you're just not supposed to be doing that kind of stuff yet, especially not of that budget.
Raising money goes very slow at young age, and I encourage you, although it does suck, to wait until you're older. It doesn't last as long as you think, I've actually just been 18 for 3 months now and I'm already on enough funding to move out of the house, yet I only work one day of the week! I'm actually still processing that.
Another plus side on waiting is that you learn how to go around with money. 2000 Dollars is a lot, and I bet that future you would've loved it too if you saved that money for e.g your car as you (assumably) are going to get your license next year! I can promise you, you'll be able to take this trip at a better moment in time. :)

oh gosh