Hello,
Pregnancy occurs only during the time of ovulation. Ovulation is the release of a single, mature egg from a follicle that developed in the ovary. It usually occurs regularly, around day 14 of a 28-day menstrual cycle. It is seen that pregnancy only occurs if intercourse occurs within the 6 days prior to and including ovulation.
Hence having unprotected intercourse on the 15th day of menstrual cycle may result in pregnancy.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
If your periods are regular yes you can get pregnant 15 days after your period.