Here is the bottom line.

You are still several years short of the age of majority. That means that if your parents say no, it's no. They don't have to give you a reason and they don't have to justify their decision. You are still too young to realize that when a 19 year old is interested in a 15 year old, either he is exceptionally immature for his age or he has an agenda he's not telling you about, and one that would not be in your best interests. Don't bother telling me that I don't know him, or you, and it's not like that and you're more mature than the average 15 year old and all that rigamarole. Heard it all before and it's only proving my point.

And yes, there are things he could legally be charged with even if you don't have sex under the right (or wrong) circumstances.