First I'd like to say at 15, you should be proud that he still a virgin as some girls your age are not also it was a thing in the past as a teenage u was frown on if you had not had sex yet at your age it's more exciting and means more when you have your first experience with someone u really love ok never let any guy pressure you into sex no matter they say.second u Will know a orgasmed feeling as when u climax your body tightens up and a fantastic feeling all over your body it is also not shameful to masturbate don't panick that u have not had peroid some girls can be late or it can be down to stress if your doing exams or probs at home if often late then speak to ur doctor to put ur mind at ease I'm older than u and I masturbate maybe at least once a week as I've split up with my partner I felt it was dirty but it is safe and healthy being a guy helps me from chances of prostate cancer I'd rather do it myself then just sleep around again don't be ashamed and second if ur worried go to your doctor's they will not tell us parents if that's what your scared of.
peace all and thanks!