You will have to clear passport control and pick up your luggage before rechecking in with RJ. Even if you have a delay on your inbound flight leaving you 2 hours for connecting, this should be doable. Cutting it to 1.30h might be tight and more than that you could be in trouble....
Arrivals is one floor down from departures, but all located within the same terminal. If you are premium customer, the premium check in for RJ is sort of separated from all regular check-in area - you just have to look out for it.

The airport can be very crowded and if you have lounge access, the TunisAir lounge used by RJ is nothing to shout about, however still much better compared to waiting in the terminal/gate itself.

All above based on my experience 2 months ago.

Cheers!