Dardar94 ,  Be honest your with current Girlfriend , break it off with her ,tell her you are not ready to be in a committed relationship .  Then you are free to pursue a possible relationship with this other girl without being dishonest and disrespectful to your current Girlfriend .  And at 15 you are not ready for a committed relationship , but this does not mean you should not accept the responsibility you have to your current Girlfriend to be honest with her .