Coinkadinkally and according to the Wikipedia:
Etymology
The name Tu BiShvat is derived from the Hebrew date of the holiday, which occurs on the fifteenth day of Shevat. "Tu" stands for the Hebrew letters Tet and Vav, which together have the numerical value of 9 and 6, adding up to 15.[2] Tu BiShvat is a relatively recent name; the date was originally called "Ḥamisha Asar BiShvat" (חמשה-עשר בשבט), which means "Fifteenth of Shevat".[3]