I am sorry for your sad childhood, and adolescence. I am not of that much experience, i have issues with my mom too, but i have some idea about life. I am pretty sure that no parent give birth to a child to "use him". Maybe your mom thinks that she is protecting you with her huge pressure, maybe this is how she was raised up, maybe she thinks that this is for your own good. On the other hand, her way of treating you is not appropriate, and as a 15 years old you have to try to talk to her, tell her all what you feel, tell her that you want to make her proud, but her way of getting angry and hitting you is making you scared of her and uncomfortable at your own home with your own mother. Tell her that you want a normal relationship, tell her that you appreciate everything that she does for you, but she also has to appreciate all your efforts especially at school. Not to mention that your mom has this thing about being better than others, socially i mean, she wants to show off infront of other mothers maybe, i don't know, but if she really needs to show off, let her do so with her own skills, not with her son's grades. And you have to know something... you are studying hard for your own benefit, not for anybody else. Work hard for YOURSELF. Your mother isn't the one studying 10 hours per day. You are the one. Start thinking about yourself, your future, what you want in life... share it with your mom... don't let her complexes (being the BEST in front of other people, and showing off...) destroy your personality... As you grow up, you will manage to avoid things that drives her mad, and try to show her that you can take decisions, but slowly slowly bcz she will feel that she is loosing you and start her pressure all over again and worse than before.
One last advice, stop googling and searching, try to find a way out deep in your heart and in your mother's heart, I am sure she loves you, maybe she lost control of herself and tries to control you, maybe she was abused as a child or she was raised this way.
God Bless you and help you!