Out of the Blue 5 is the second time in recorded history that Grand Finals has gone to Game 15
The first was Royal Flush in 2016 between Mango and Armada.
It's technically possible that one or more of the 2004/5 tournaments went to game 15, but much of the bracket data from those tournaments has been lost, and MLG rules at the time made game 15s impossible at those events.
u/johneaston1 — 17 hours ago