Here is the quintessential Jewish question: How do we emulate God? We are told that we were created by God. We are told that we have a divine spark within us.
"Tu" (the Hebrew abbreviation of 15th) in the month of Shvat was set (Hillel's opinion generally overrules Shammai's) as the beginning of the tithable year for tree fruit: Calculating the tithe on fruit starts again for fruit that sets after that date.
Coming a month and a half before the spring equinox and two months before Passover, Tu BiShvat provides a glimmer of springtime at a time when winter can often be at its cruelest.
"15th of Shevat;" New Year of the Trees; Jewish Arbor Day, which is a minor festival.