The desire for pornography does not go away once you are in a physical relationship with someone else. Masturbation only further isolates you from your partner and when there is isolation, the relationship suffers. Just because you are 15 doesn't mean it's okay. The time will come when you will want to be in a relationship with someone and if you want a good one you don't want to go into it with shameful habits or hiding things from them. This was the main reason for my own divorce.