Even the stuff that's common in both series are quite different, you've probably read the other comments talking about mainline SMT focusing on dungeons and thinking "oh god, no" because the Persona dungeons suck, but the thing is that there's not a single dungeon in Persona that come close to the average SMT dungeon, to give you an idea, you'll seriously start considering using pen and paper to guide yourself once you notice the dungeons clearly want you to understand them and won't let you stumble into solutions, the unfortunate side effect of more complex dungeons is that when they are badly designed you really notice it though generally won't sour the experience