You have gotten some good advice here.
No matter how mature you think are right now at 15 I can assure you that you will see it differently in a couple of years.
The purpose of dating is for finding a future mate and personally I don't think that most teens are ready for marriage mentally, emotionally, spiritually.
Also you ask about dating a friend. Too many people start off with the wrong foundation for dating. Most people go from aquaintances to dating and most end up with broken hearts/relationships/emotional scars and then wonder what happened.

Too many people are loose with their words/hearts/emotions in a relationship.
The Bible tells us to guard our heart and with good reason.
To have the right relationship a couple should build it as friends first then good friends to best friends and then dating IMO.
The first thing a person should do is pray, pray, pray about their relationships. 