What is a good RPG to play for sessions of 2 hours or less?
That depends on what you want to get out of the experience, of course. If you want an epic story, then sessions of two hours simply don’t cut it because there is too little time to ramp up and ramp down again. At least, that’s my experience playing The One Ring with 2 hour sessions — it just didn’t work.
So you’d need something where every session is kind-of self-contained and that maintains the “narrative thrust” all throughout the session. No downtime, just a no-holds-barred action-packed story that keeps the players engaged.
Maybe The Sprawl could work like that, if you have a strict time-keeping mechanism in place. Maybe Blades in the Dark could work, because it focuses on the action so much, and downtime could be played through e-mail or something like that. Or maybe Ryuutama, if you have short journeys and simple problems to solve.
But I think the game that is best for this is Paranoia. It sets the players up against each other, which means everybody has to be fully engaged with what is happening — otherwise they will, quite literally, lose out. Paranoia scenarios don’t need a real plot or a real resolution: just give the players some random weapons, put them in a semi-isolated location, and watch the fireworks unfold. And after two hours, time is up, the Internal Security goons arrive and mop up any survivors — the end.