It is very normal to get pregnant 15 hours after ovulation because the egg will be picked up by the umbrella end of the fallopian tube in about 10 minutes after ovulation and put into the fallopian tube where it will wait for the sperm. After intercourse, the sperm will reach the fallopian tube and combine with the egg to form a fertilized egg after 6 hours at the latest, so it is very normal to have intercourse 15 hours after ovulation to get pregnant. If you have intercourse 24 hours after ovulation, the chances of getting pregnant are almost zero because the egg will die if it is not fertilized within 24 hours after it is discharged.