'Fifteenth' in the Bible

The Feast of Unleavened Bread to the Lord is on the fifteenth day of the same month; for seven days you shall eat unleavened bread.

“Say to the children of Israel, ‘On the fifteenth day of this seventh month, and for seven days, is the Feast of Booths (Tabernacles) to the Lord.

‘On exactly the fifteenth day of the seventh month (nearly October), when you have gathered in the crops of the land, you shall celebrate the feast of the Lord for seven days, with a Sabbath rest on the first day and a Sabbath rest on the eighth day.