Paul's ship anchored safely in fifteen fathoms on the 14th day, after thirteen days of toil and trial, Acts 27:21.
On the fifteenth day of the first month was the feast of unleavened bread, Leviticus 23:6
On the fifteenth day of the seventh month was the feast of Tabernacles (Leviticus 23:34).
Additional commentary on the Biblical Meaning of 15 *
In Scripture the number 15 pictures rest, which comes after deliverance, represented by fourteen.
The 15th day of the first month is the first day of the Feast of Unleavened Bread, a day of rest for the children of Israel. The 15th day of the 7th month begins the Feast of Tabernacles, also a day of rest.
God delivered Israel’s firstborn from death on the 14th; then, at the beginning of the 15th day at sunset, the children of Israel began to leave Egypt by night. This night is called 'the night to be much observed unto the Lord' (Exodus 12:40-42; Numbers 33:3; Deuteronomy 16:1). On this same day 430 years earlier, after the sun had gone down ending the 14th, God told Abraham in a vision that his descendants through Isaac would end up as slaves in a foreign country - but that He would release them from this bondage after 400 years (Genesis 15:12-16). Exactly 430 years later - on the same night - this prophecy was fulfilled as the children of Israel left Egypt on the 15th day of the first month (Exodus 12:40-41). On the same night - in order to guarantee His covenant promises to Abraham - the Lord passed between the parts of sacrificial animals, as evidenced by a burning lamp and a smoking furnace, which wholly consumed the sacrifices (Genesis 15:17-20). In performing this ceremony, God was pledging His future death as the perfect sacrifice for the sins of the world - guaranteeing the future 'rest' from sin for all who inherit eternal life.
On the same day as Abraham's vision and the children of Israel leaving Egypt, the 15th day of the first month in 30 A.D., as the sun was setting to end the 14th - Jesus’ body was placed in the tomb. Thus, Jesus began His three days and three nights in the heart of the earth.
Rest from our sins and the sins in the world
For Christians, the 15th day of the first month, the first day of the Feast of Unleavened Bread, pictures rest from their sins, having had them removed by Christ’s shed blood on the 14th.
The 15th day of the 7th month begins the Feast of Tabernacles. For the children of Israel, it pictured rest from the long harvest season. They were to dwell in booths in remembrance of their trek in the wilderness.
Prophetically, the 15th day of the 7th month pictures the coming Millennium when the world will have rest from sin because of the binding of Satan on the Day of Atonement. Under Christ’s reign, salvation will then be offered to all the world - the great spiritual harvest of God for 1,000 years.