@Inlovewithher,
I tell my kids that the most important thing is that you are in a respectful, equal relationship. It might be good to wait a couple of years, because you do get more emotionally experienced.
If you are in a caring relationship where you both listen to each other and respect each other I think it is fine. Sexual relationships come with really strong feelings, you need to be mature enough to handle them... and to be honest, relationships between 15 year olds can be great, but you should be realistic. Is it quite possible you and your girlfriend will break up at some point, you should be realistic about that.
Relationships come with a range of emotions, some are great, some hurt. That is the nature of sexual relationships. If you are going to jump into this part of adult life, you need to be willing to accept that sometimes breakups hurt a lot. Sex makes these feelings even more intense. (The good news is that we all go through this, and we all survive and move on.)
I think people are overreacting a bit about the doctor part. Birth control is a real issue, condoms are not perfect (but provide protection from some diseases). Birth control pills work well if your girlfriend is good about taking them. Many people (including myself) think IUDs are great; they work very well and can be taken out when she wants a baby.
But honestly, other than condoms, birth control choices belong to your girlfriend and her doctor. Be supportive of her decisions.