'Fifteenth' in the Bible

On the fifteenth day of this month there will be a festival; unleavened bread is to be eaten for seven days.

“You are to hold a sacred assembly on the fifteenth day of the seventh month; you must not do any daily work. You are to celebrate a seven-day festival for the Lord.

They departed from Rameses in the first month, on the fifteenth day of the month. On the day after the Passover the Israelites went out triumphantly in the sight of all the Egyptians.