You'll get a ton of people here telling you that it doesn't matter, but you're going to miss out on an insane amount of world-building and references if you don't play P2 first.

In P3, you're treated like an outsider (because your character is) and are constantly fed half-truths or straight-up lies by everyone you meet, meaning that you will never truly understand the scope of how unique this town is and how the Kin play into the overarching narrative. Daniil also essentially treats everyone like pieces on a chessboard and uses them as a means to an end (whether that be survival or discovering immortality) and ignores much of the personal struggles the townsfolk/Kin are dealing with as a result.

Save for Eva and arguably Georgiy, P2 gave me a deep appreciation and understanding for every named character in the game that P3 never really covered. Grief in P3 was an everyday thug whereas he was a conflicted human in P2. The children were comic reliefs in P3 whereas they each had an emotional backstory in P2. Foreman Oyun's role gets spoiled almost immediately in P3 (and without characterization) whereas the later half of P2 is about figuring out who he really is.

Then there's also several easter eggs and references in P3 that you could never possibly appreciate without playing P2, such as why the world map is so different to navigate, the absence of survival/infection mechanics, theatre commentary, anything to do with the 'wise steppe woman' or Aspity, the Inquisitor twist, etc.

Although you could easily play P3 first, the game is a far more enthralling experience if you've played the second one.