「You sound like, " Why choose to live in a dorm, when you have your own house?"
I also have my reasons as to why I want to study in Japan. I just want to know the process」
At the risk of sounding mean, that's a question you absolutely have to be able to answer if you want to live in Japan, and how you answer it will determine the process you need to go through in order to live there.
In order to live in a foreign country (i.e. a country that you are not a citizen of), you need a visa, and in order to get a visa, you need a reason, and depending on the reason, the process for obtaining a visa is different. From the Japanese government's perspective, you already have a place to live and study in your home country, so why do you want to live and study in Japan? Do your parents, on whom you're dependent for food, shelter, etc. live in Japan, and you have to move there to be with them? Are you applying to some sort field of study that doesn't exist, or only exists at a very low level, in your home country? Do you have to leave your country as a refuge or to seek political asylum?
Unfortunately, "I just really like Japan and am interested in the culture" usually isn't considered reason enough for a long-term visa. There are student exchange and homestay programs that reason will qualify you for, but they tend to be at most a year in length, and you've already said you're not interested in them due to their cost.
「Even if I was rich( I wish), you're saying scholarship is not for me cause I'm financially stable. Everyone has their own problems that they're going through. Or it can be that they just don't to be a burden anymore. Over-thinkers tend to over think that they are burden in others. 」
Pretty much every scholarship is tied to some set of conditions, and often one of those conditions is financial need. Yes, there are also some scholarships that are based only an academic merit, but there are no scholarships that are actively seeking applicants who are simply "overthinkers who don't want to be a burden."
Honestly, at this point in your plan it sounds like you're over-focusing on the financial/scholarship aspect, since you seem to think that's the next step after having good grades and finding a home to stay in in Japan. Really, though, the big hurdle you're facing is obtaining a visa, and figuring out how to do that is going to depend on how you answer the question "Why do you want to live in Japan?"
「I can't ask my parents 'cause they're so busy at work and me who doesn't want to bother them.」
Again, at the risk of sounding like I'm stepping on your dreams, if you can't find/make time to talk with your parents about this, you're probably going to have to wait a few years, until you're a legal adult, to live/study in Japan. At the age of 15, you'd be a minor in the Japanese legal system, and so any residence status you'd be applying for in Japan will require extensive cooperation from your parents.
And once more, I apologize if my, or the other users' responses, sound overly harsh. We often get queries from teens who have an interest in Japanese culture/society and think that the main things they need to live in Japan are an adult willing to let them live with them and money for living expenses. Really, though, the much larger, more important things are obtaining a visa and being proficient enough in Japanese to keep up with high school-level classes designed for native Japanese-speakers. Many teens vastly underestimate how difficult those will be and fixate on finding a place to stay and scholarships.
Learning enough Japanese to function in a regular Japanese high school class takes several years, and obtaining a multi-year visa that will let you go through all three years of Japanese high school is very unlikely if your parents don't live in Japan. The more realistic option is a student exchange program, which would generally be for a year or less, but you've said you don't want to do an exchange program. Alternatively, as mfedley mentioned, you could apply to an international school, but those tend to be very expensive, and then there's the question of how "Japanese" the experience would be if many of your classmates aren't Japanese and your lessons are taught in English.
Really, it sounds like the best option for you would probably be to wait until you finish high school, then obtain a student visa to come to Japan as a language school student for a year or two. Like international school, this would unfortunately mean that your classmates would not be Japanese, but language schools are much more affordable, and many foreigners who move to Japan then transition to a regular Japanese university. If that doesn’t sound appealing to you, you might want t reconsider exchange programs if you’ve really got your heart set on studying in Japan ASAP.