Passover is the 14th, and the starting point. According to verses 2 and 3, it was in Rameses, not their houses. It was the night part of the 15th day of the month that they left Egypt. It was the 15th day of the first month, on the day after the Passover.
The Egyptians would not have been burying their dead just minutes after they died on the 14th in the dead of night. They were burying their dead late on the daylight portion of the 14th toward sunset, as the Israelites were beginning to move out of Rameses. That is four differences already.
