15 year old moving to japan

I was wanting to move to Japan, but I'm only 15 and still learning Japanese. I just want to live there and go to High School there, then move back to the US to family. Would I be allowed to work (so I can afford living costs) and live in Japan despite being only 15 and not knowing Japanese (I am still learning, but it will be a while before I actually move to Japan, so I believe i can become more fluent during that time, plus living in Japan will help in my studies)

Dude, you don't know how to speak/read/write Japanese fluently, you apparently don't have money to live there on your own, there won't be many options for you to work as a high schooler and without knowing Japanese, and I take it that you don't have any relatives or family there to take care of you.

Unless you're referring to a short-term student exchange, NO CHANCE. Just wait a few years until you get to college and then start coming up with feasible ideas.

Unless you come on a student exchange, there is no visa that will allow you to stay in Japan by yourself. Have you looked into the costs of setting up in Japan? Just to move into an apartment here you must pay around 6 months rent (key money, deposit, agency fee, 2 months rent in advance), which in Tokyo usually means around $5,000 plus, just to get into the apartment.

Most high schools do not allow students to work as it distracts from their studies, and I doubt that any high school would accept a foreign student living alone without relatives.

Unless you can find an exchange program to sponsor you (and there are plenty around, so start researching), your idea is impractical for many reasons- keep your dream of coming to Japan, but wait until you have finished high school and can come to Japan as a university student to study, which is much more possible. Start saving now though, Japan is not a cheap country to live in!