Just because you are 15 and your parents don't know doesn't mean that you shouldn't go to hospital. You feel unsafe therefore you need to go to a place that you can, or be around people that can force you to be safe. Tell your parents. In the long run you will be grateful for it. And to be blunt, when they find you dead and they think that if you'd just come to them that'd you'd still be with them, it'd break their hearts. They may be upset, but it is because they love you and want you to be safe. Don't throw that away because you are afraid of their reaction. Been there, done that. It is 99% of the time worse in your head. Take care of yourself, if not for yourself then for them.