The number 15 symbolizes rest, deliverance, and divine grace in biblical and Jewish tradition.
In Jewish tradition, Tu BiShvat (the 15th of the month of Shvat) is celebrated as the New Year for Trees, and the 15th of Nisan marks the beginning of Passover—the celebration of deliverance from Egypt. The number is also linked to the 15 Songs of Ascents (Shir HaMaalot), Psalms 120–134, which were sung on the steps in the temple in Jerusalem. The full moon, which falls on the 15th day of each month in the Hebrew calendar, underscores the number's connection to fullness, completion, and divine blessing. The Hebrew letters Yod (10) and He (5) together form the numerical value 15 and at the same time constitute the first two letters of God's name (YHWH). Out of reverence for God's name, Jewish tradition therefore writes the number 15 as Tet-Vav (9+6) instead of Yod-He. According to rabbinic tradition, the 15 Songs of Ascents (Shir HaMaalot) were sung by the Levites on the 15 steps between the Women's Court and the Israelite Court in the temple. The number of steps corresponded with the number of psalms. Tu BiShvat, which means 'the 15th of Shvat,' is observed as the New Year for Trees and originates in the Mishnah (Rosh Hashanah 1:1), where it discusses which date should serve as the cutoff point for tithing fruit trees.*