Interesting discussion, Xenoki. I like it that you and your friend are talking things out, as well as RPing and exploring your boundaries.
In your eyes, and in mine, I am an old man.
When I was a teen, I suppose I would have been frightened by situations too potentially dangerous to me. But pretty much, a teen aged heterosexual boy went as far as he could until the girl said no, stop.
I wish I could say I was more mature, but I wasn't. And my sexual history was not exactly as a predator, either, since females have always taught me. I'd like to think that I've been appreciative and sensitive to them, but I know that they were wiser - from birth, do you think?
However, what I want to say is this. I'm not trying to say that things are the same for you as they were for me back in the "olden days."
But what I think you need to be prepared for is this:
Where I depended upon the female to stop us, and felt like "going ahead" was what males were supposed to at least "try" to do; it sounds like to me that you are shaping up to be the one who will need to know when and how to stop.
And no matter that most 15-year-olds probably know much more than I knew at that age (but possibly not, as the physiology and mechanics are the same) - the point is that a male teen's hormones are going to send a completely different signal than what you may plan now.
I applaud you for being responsible in your relationship. And here's hoping you don't mind an old man's rambling.
Marge is the love of my life.