I have no idea what it's like to HAVE a 15 year old girl so you can take my advice with a grain of salt, but I do remember what it was like to be one! I wish my parents had focused more on how to pick a good boyfriend than assuming that all of them were no good. I wish somebody had told me that dating - actually going on dates and getting to know someone - is really fun! And that relationships aren't only about sex - I think that was the message I got as a teenager. I think I also would have benefited from someone talking to me about what was appropriate at that age (some kissing?) and how to make sure I didn't get myself in a situation where more happened - whether it was willingly or not. I think it's harder to cross the line when someone has told you very specifically where that line is, and also what to do if you get close. But that's an uncomfortable conversation to have.
I guess the bottom line for me is, if all boys just want sex, isn't the risk that she just picks one of them for a boyfriend and doesn't look for the ones who, yes, may want it, but are actually respectful enough to not push it?
I know you don't like her friends (I wouldn't either!) but she may learn some hard lessons through their choices instead of having to do it on her own. Hopefully you can encourage her to find some other friends too. I did have a lot of male friends in high school and WOW was that helpful to understand what boys are like! Not just how much they want to have sex, but also that they had some of the same fears and that they got their hearts broken just like the girls. I had only a few close female friends, but all of them are still my friends today and the kind of women I could call in the middle of the night for help. Good luck!
Edit: I just saw YOUR edit. The boys probably see her as better than the other girls. I would almost guarantee that at least on of them has a huge crush on her but they are afraid because they see her as a real person and not a sex object. I think I was like your daughter - I thought the boys didn't like me either. In reality, they just liked me more as a person than the other girls, but you're right, that's hard when you are a teenager and want the boys to think you are pretty. I'm sure they do - they just respect her more! You're right, it is probably for the best, but if she's brave, she could hint to the boys that nobody is interested in her as a girl. I bet she'll be surprised how untrue that is.