Ay, scary yan talaga sis! So 15 days delayed ka na pero negative pa ang PT, honestly, I'd suggest makakuha ng appointment sa doctor na para ma-check properly, kasi sometimes it takes longer for hormones to show up sa test, or baka may iba pang nangyari sa cycle mo after stopping pills. A few of us mums had delayed periods din after going off contraceptives kaya normal lang, pero since medically speaking it's been two weeks na, better safe to get a proper check-up or blood test para ma-confirm na talaga at peace of mind mo na.