Don't do this to yourself.
The likelihood of it being a high school setting is significantly higher than anything else.
Honestly I feel like you guys are hoping for Atlus to think of it in a Western fashion. I recently put the same question as to why more anime didn't take place in college and I got swiftly told that for the Japanese, High school is the best youngster memory. Unlike the west where college tends to be remembered more fondly than High school, college in Japan is very technical. Go to lecture, come out, maybe a club but not likely. It's not as cherished as high school.
In fact in terms of anime there is only one currently airing one that takes place in college and before that one I genuinely can't remember the last slice of life that took place in college.
But that's besides the point, the discussion here is people are reading TOO much into the image. The theme of the game is probably going to be about escaping something or feeling a prisoner to something. This'll probably be the theme of the Personas (P4's themes were stuff like not accepting an aspect of your true self).
If this took place in jail, social links and the dating sim aspect would be all but gone considering you wouldn't be able to leave the general area. If this took place in juvie they'd have to explain EXTREMELY well why all these kids with different personalities that aren't entirely delinquents are in there.
High school is the safest best for Atlus. Their two previous Persona games, which happen to be their most popular titles, take place in high school. Many slice of life anime takes place in high school. The light hearted tropes such as bath house and beach scene will probably make a return.
Persona's chances of dropping the more light-hearted high school sol anime adventures are extremely slim. Appealing to the few of you who want Persona to get all nitty gritty when Atlus clearly already has a long-running franchise, which persona is a part of, would be dumb in terms of profit. Persona is as popular as it is for a reason. While it being an over-all amazing game is obviously a huge part I'd like to argue that the dating sim/happy go lucky outside world setting is another big reason it does as well as it does.