'Fifteenth' in the Bible

and Jeroboam maketh a festival in the eighth month, in the fifteenth day of the month, like the festival that is in Judah, and he offereth on the altar -- so did he in Beth-El -- to sacrifice to the calves which he made, and he hath appointed in Beth-El the priests of the high places that he made.

And he offereth up on the altar that he made in Beth-El, on the fifteenth day of the eighth month, in the month that he devised of his own heart, and he maketh a festival to the sons of Israel, and offereth on the altar -- to make perfume.