Misses period 15 days all test have been negative yes i have had unprotected sex in the last 3 wks is it possible i ovulated late and could be preg?

Not likely pregnant: with neg HPT this far out. Reasons for missed / late period include: an anovulatory cycle in which no egg is released, marked v or ^ in weight; eating disorder; Over-exercising (endurance athletics), stress, travel, significant illnesses, oral contraceptives & other meds, Illegal drug use, breast feeding, hormone imbalances and medical problems (i.e., PCOS). Pregnancy is #1 reason.

Very unlikely: Most urine pregnancy tests are very accurate, and if performed and interpreted correctly, tend to be positive within days after conception. If you remain unsure, do another test in 1 week if you still have not started a period. It is not unusual for a woman to be irregular, late, and/or miss a period occasionally for not apparent reason.