hi.Follicle size and ET both are good, rather 28mm is a larger size. You should have followed ovulation study to see whether the follicle ruptured or it became cyst
after further enlargement. If size still grown and no rupture of follicle then chances of pregnancy
are not there. But if growth upto this size and follicle ruptured on day 12 or 13th acc. to your report, then some chances of pregnancy as egg remains viable for 24 hours and you had intercourse on 15 th day.