'Fifteenth' in the Bible

and in the fifteenth day of this month is a festival, seven days unleavened food is eaten;

'And on the fifteenth day of the seventh month a holy convocation ye have; ye do no servile work; and ye have celebrated a festival to Jehovah seven days,

And they journey from Rameses in the first month, on the fifteenth day of the first month, on the morrow of the passover have the sons of Israel gone out with a high hand, before the eyes of all the Egyptians --