I believe Persona Q & Q2 both take place before any major events really take place in any of the 3 persona games, so no endings or whatnot would be spoiled.
There actually are some minor spoilers, but it's mostly character-related. For example, Naoto's secret in P4 is revealed. You won't be spoiled story-wise though iirc. Essentially what Haru said.
Gameplay-wise, however, don't come in expecting a Persona game. It's a weird Persona/Etrian Odyssey crossover. First-person dungeon crawling, overpowered map bosses you definitely shouldn't fight when you first meet, new skills, everyone being able to equip "sub-personas" but not switch personas... Just be prepared for whiplash.
overpowered map bosses you definitely shouldn't fight when you first meet
I can 100% confirm this is the case. Unless you're some god at these kinda of games there's a rare chance you'll get past the first labyrinth's boss. And that damn burning beetle...