If you miss your connection, you'll get put on the next train on to your destination - assuming you were trying to make it. You have reserved seats on all of these trains, so you don't have to clamor to get a seat like you would on a regional train.
Check the schedules. If there are other trains on to Salerno after yours that you would get you there at a reasonable time, then don't worry about it.
Fifteen minutes should be plenty of time if you don't dwaddle. Use the bathroom on the train - don't expect to use it at the station.
If you will have a working smart phone, install the Trenit app on it. Then you can find out the platform information for the next train from you phone before you even get off the first train. And you can confirm that the train you are on is on schedule.
Sometimes the next train is on an adjacent platform and you just cross over and get off one train and on to another - that has happened to me a few times. Sometimes you have to take stairs down and under the tracks (look for an elevator, up at least). Cross your fingers.