Can you first start feeling whiplash pain 14 or 15 hours after a car accident?

Yes. A whiplash is a muscle strain or pull. Lika any muscle injury, it often feels worse 12-18 hours after the injury occurs.
Yes. Often the pain and symptoms of whiplash can appear immediately or take hours, days, weeks or even months to manifest. The symptoms are many and often depend on the type of whiplash (flexion/extension, ) and how you might of suffered the whiplash- sports, car accident-hit from front/side/rear/passenger/driver.) tmj/tmd is a major symptom of whiplash as the jaw can be thrust open from the accident.
Yes. It takes time to develop edema. Need an MRI to find out where there may be structural damage.