'Fifteenth' in the Bible

And on the fifteenth day of this month is the feast; seven days shall unleavened bread be eaten.

And on the fifteenth day of the seventh month ye shall have a holy convocation: no manner of servile work shall ye do; and ye shall celebrate a feast to Jehovah seven days;

They journeyed from Rameses in the first month, on the fifteenth day of the first month. On the morrow after the passover the children of Israel went out with a high hand in the sight of all the Egyptians.