According to howlongtobeat.com a completionist playthrough of Pillars of Eternity 2 takes 49 hours, while a simple "main + extra" run might be polished off in 42.5. Meanwhile, a speedrunner named Onin has got it down to 26 minutes and 25 seconds, on Paths of the Damned difficulty to boot.
That said, this is a speedrun made possible by using blessings that are unlocked during previous playthroughs. It's a kind of New Game Plus option that lets you restart at higher level with better gear and stats than you'd normally have. And playing on Paths of the Damned rather than Easy makes it possible to lose one specific fight very quickly, saving some more time.
Onin played as a rogue and stealthed away from a lot of fights, but because the fighter companion Eder isn't sneaky enough he became a liability. So Onin killed him at the start of the game. Other clever ways of speeding things up included triggering combat as a way of skipping certain cutscenes, and duping gold by stealing items back from a merchant then selling them over and over again. That's a much easier way to get yourself a ship worth 105,000 gold than doing all those sidequests.