I'm only a few years older than you, so I'll try to be nice because I know where you are. You, at 15 years old, might love your boyfriend now. But your 15 year old self isn't going to be the same person you are going to be, say in 5 years, when you are 20. 5 years isn't the longest amount of time, but as an individual, you will change immensely in those 5 years. The person you are today will be a thing of the past, and your likes and dislikes will completely change. The same thing will happen with your boyfriend. So, yes, at 15 you can love each other as 15 year olds can. But at this age don't assume that you will be with him forever. Yes, you might, because that happens too, but there is a better chance that as you grow and change, your relationship will change as well. You may realize you love him more, or you may realize that you are not as perfect for each other that you originally believed.
However, you seem really mature and with a good head on your shoulders, so you have a good chance of making good decisions and being ok.