Well, let's see... if I was a parent and had a 15 year old daughter, I'd be nervous about her dating an older guy in the first place. Then if she snuck out late to be somewhere with him, and I didn't know where they were or what they had been up to... well, just put yourself in his shoes...
What if he went to check on her for some reason and found her gone? And you haven't said anything about what was going on in the car... if I see my daugter coming back from sneaking out, making out with an older guy in his car... well, I probably wouldn't hit him. But I'd be pretty pissed and can't say (without hearing both sides) that I necessarily blame this guy for "assaulting" you (did it even hurt?).
On top of all that, it sounds like you were well-aware that she was sneaking out, which just isn't cool. It's disrespectful... and if you care at all about the girl then you should care about her parents' wishes (which to my knowledge werent' unreasonable). I can't believe you have the nerve to try to sue or press charges after this... that's about as logical as him pressing charges for kidnapping or something. Good lord... what you should be doing is apologizing for taking his daughter out past curfew.
I mean, damn, am I alone here or does anyone else hear crap like this and feel like society's on a downward spiral?