There is so much wrong in this post I don't know where to start.
1) Sex isn't (or shouldn't be) the only reason you're interested in girls.
2) We shouldn't be assuming that they're going to have sex on the first date anyways, especially since they're 15.
Good thing I didn't say either of those things then huh
Also, sex IS the reason men and women are interested in each other...our bodies are reproduction machines
3) If you need "cool friends" to get a girl, she's not worth your time. If she doesn't like you for who you are, you should just forget it.
This is good advice for some people and TERRIBLE advice for others. Fact is, some people as they are, are not gonna get any chicks. So they can just stay the way they are because everyone keeps telling them to be themselves, or else they can clean themselves up, whip their life into shape, make themself into somebody that other people want to be around, and enjoy the benefits. If you feel like something is part of your identity, sure, go ahead and cherish it (unless you'd rather get girls). But I'm pretty sure most of the things that stand between awkward guys and getting girls are not stuff they'd consider an important part of their self-concept.
One thing's for certain, the OP has given us enough information to know that he is not currently prime beefcake, and if he wants that to change, telling him to just be himself and stay the same ain't gonna help.
Of course you need to move away from the dork-zoid zone, but you should never try to be someone who you aren't for a girl. If you do, it ends badly.
But what does it mean to "be someone you aren't?" Does it depend on what you define yourself as? Or what others see you as? And where do you draw the line between characteristics that you have to keep the same because changing them would be "trying to be someone you're not", and characteristics that repulse people and have got to go? What if they're one and the same?
If you're a shy and awkward teenager, then it may feel like it's "not you" to go to parties, go up to people and shoot the shit and make new friends, flirt idly with girls, show off, and so on, but do you want to stay shy and awkward forever?
And as for having cool friends, sure, if you hate them don't hang out with them. But nobody wants to have fewer friends, at least past a certain point. And being around cool people makes you meet more cool people, and associating with cool people makes you more attractive to girls. That's a fact. You can define "cool" however you want.
4) If she likes you for your "cool friends," that should be ringing alarm bells all over the place.
Here's another thing about female psychology (well, human psychology in general) - the reasons why people think or feel a certain way are not necessarily known to the people in question. If you see a girl you like, for example, you just see her, perceive her as hot and an interesting person, and there it is. You don't analyze her facial features and body shape and compare them to an ideal model in order to calculate her hotness in a formula. Same goes for girls. They see a guy and they think he's hot. They don't think, (with a few exceptions) "this is a guy who's well-dressed, popular, comfortable in social situations and self-confident, has talent and prospects and money, I guess I should be attracted to him." People feel as if they're attracted to others for no other reason than that the person just seems right to them, but that isn't the ultimate level of causation. Girls brush their hair and put on makeup and sexy clothes to attract men, and men do all that stuff I listed above to attract women.
So yeah, don't pretend to be a person that you're not...except if you need to. If you need to pretend to be a confident studly dude, then if you start acting like one, you will become one. If you consider that betraying your true self, then whatever. Mating is a marketplace and you're not increasing your stock value by telling yourself you're more "real" than all the other guys around you who are getting all the women.
btw another benefit of cool friends is they can teach you how to be less of a tool