While some may say that age is nothing but a number, I disagree. Time (age) gives you a different perspective than what you see right now. Time also gives you maturity and the tools to know how to handle situations.
I have dated a couple guys way outta my (age) league. I was 12, he was 16...another, I was 15, he was 21.
The first one...he was basically desperate. Not good looking by any stretch of imagination...but I went with him because I was flattered because he was "older" an in High school. He happened to be my friends brother. Nothing ever happened between us, but that was purely because I wasn't ready and always said no.
The second one, well, that was illegal. He was legally an adult, and I was not. While I will admit he was my first "love", the relationship was really not a healthy one. He was my ticket to all sorts of things a 15 year old has no business involved in.....sex (ok, so it was the best of my life), drugs and a whole lot of alcohol. (note...my parents DID NOT know of this one. I snuck out everynight, or snuck him in. I'm pretty sure I'd still be locked in a convent to this day if they would have ever found out). He also had 6 years of living and learning on me. Because of that, he knew a whole other world that I desperately wanted to know. 15 is a scary age as it is, without trying to grasp things that you shouldn't even be faced with yet. Speaking from experience, they will break your heart harder than someone within your own age range.
After you are an adult, I really say that anything goes. If there is something a 20 year old sees in a 50 year old, then whatever, that's their business. But an adult has no business being with a kid. Period. If said adult is really into said kid, then a few years will be worth the wait. Otherwise, that's called statutory rape (well, not in Illinois...there is no charge of statutory rape anymore...it's just called pedophilia). Not saying you are going to sleep with these guys, but again, speaking from experience, you will find yourself doing things to make yourself "older" or "mature" so you will feel like a contemporary to them. I made myself grow up way faster than I had to and sometimes I really regret it.
basically what I am saying is, be with boys your own age. 15 is really young to be dating anyone outside the 14-17 year old range IMO. You have your entire life ahead of you. The boys will still be there.