I'm very sorry to read this story, its not okay that your ex-boyfriend not only hit you but he also raped you. If you do go to the police most likely he will be put in a corrections facility and will most likely be registered as a sex offender depending on where you live; only because you are 15 years old and that in I believe all states now is too young to have sex.
Now about the pregnancy, you have to decide what you want to do,which could either be raise the child yourself, put the child up for adoption, or abortion. It does cost a lot of money to raise a child and a lot of time and effort. I'm not too familiar with putting children up for adoption but in my state you can bring the child within a week of birth and hand it over to authorities no questions asked and they will put your child in a foster home. If you want to seek information about abortions talk to your health care provider as they can assist you through the transition and also give you information regarding the risks and cost of abortions.
Your parents could also press charges on their own being that you engaged in sexual intercourse and you are probably under the states legal age limit.
From what I have read of the situation, I think you should go to the police even though you don't want to, the simple thing is that he put you in danger, raped you at the risk of getting an std, and got you pregnant. I believe if you don't do something now, he could just go and do this all over again to you or someone else.
I hope this helps even a little and feel free to
pm me if you have any other information or need help with anything else.