Time for flight changeover in Rome

1.5 hours should not be an issue, unless your first flight is significantly delayed. When you arrive in Rome, you will likely have to go through another security check, but there are priority lines for people with short connections.

Your passport is irrelevant, since you will not have to go through any immigration, you are just transferring from outside of the EU to outside of the EU*.

The US does not have any preclearance in Rome, meaning that the boarding procedure will be just like any other flight (quick check of passport by the airliners personnel and your ticket).

Now, if your flight is delayed, the flight you are transferring to will get this information and they will take a decision to wait for you or continue, depending on various circumstances. Normally they will wait up to maximum a few tens of minutes, especially for long-haul flights where the margins on the schedules are already quite good.

While still on the flight, you can ask to be seated in the front of the plane just before landing, to help you get off quickly.

At any security checks, ask the personnel for the priority lane and show them your ticket, they will let you through if you do in fact have a short connection time.

Boarding usually closes 20 min (exact limits depend on company) before scheduled departure (departure time is the time that the airplane should start moving on the ground), but airlines are usually flexible with this as well, especially if they have received information that one of their passengers is arriving late.

The gate of all connecting flights relevant for your aircraft should be displayed on the information monitor in the airplane shortly before landing. If you cannot find it, ask the flight attendants before they are busy preparing for landing. Otherwise you should check the monitors when you arrive at the terminal, or better yet, ask at the information counter. Any staff at the airport will also be able to quickly direct you to the gate when you know it.

Now, in the unlikely event that you do miss the flight, the flight company is obliged (because the flights are on the same booking) to provide you with sustenance, a hotel room if you have to stay overnight, and rebooking to another flight that will get you to your destination. You would also be entitled to a significant monetary compensation, if the flight company is at fault for the delay: https://europa.eu/youreurope/citizens/travel/passenger-rights/air/index_en.htm#shortcut-15-compensation-cancellation

As a note, you will not have to change terminals. At FCO (which I saw in your other post is your airport), there are three terminals. Terminal 1 only serves domestic and Schengen flights Terminal 2 is closed Terminal 3 serves all non-Schengen flights https://www.roma-airport.com/terminals.php

*there are two international airports in Rome, FCO and CIA, and if you need to change airports you would have to go through immigration. However, the flight company would not provide you with a single ticket for that kind of transfer if there is only 1.5 hours of layover.

Possibly; I think it will be OK.

Be certain to tell the plane staff that you have a short layover and ask them if it is possible to leave the plane before other passengers.

Also ask them if it is possible to have the gate known for your second flight so you do not have to spend some time figuring that out while running to it.

I would think it is risky because:

1. airplanes are often late
2. it takes a lot of time to deboard a plane
3. airports can be big and confusing
4. boarding usually closes well before scheduled takeoff

On the other hand, what will happen if you miss the connection?

1. You will miss out on an important interview, event, graduation, marriage, funeral, etc - which was the sole reason for your trip.
2. You will be just one day less early than you otherwise would have been, but you will still be early.

No matter how much long the layover is, there is a non zero chance that you will miss the connection. From there it is just a matter of balancing risks and benefits.