It is a short walk and escalator ride from the Amtrak/NJ Transit platform to the AirTrain platform. The AirTrain ride from the rail station to the terminal is listed as 9 minutes to Terminal B, and between 5:00am and midnight, they should run every 3 minutes. If you want to be conservative and arrive at the terminal three hours before scheduled departure, this would mean arriving at the EWR rail station by about 14:40. Saturday evening is not an especially busy time and December 1 is not an especially busy weekend.
The problem is that Amtrak reliability is hit-and-miss. The Northeast Corridor is a very old and heavily used part of the network, and there is frequent congestion rippling out from the tunnels going into New York.
There are a couple of resources available for tracking historical performance; my current favorite is the Amtrak Status Maps Archive Database (ASMAD) which includes a searchable database. The database is not comprehensive—for example, it does not have arrival information for EWR—so I tracked departure delays from Metropark/Iselin, the previous station; as the distance between MET and EWR is short, it is not a stretch where trains can "make up" time for delays.
Looking up Saturday train 88 departures from MET for the last two months shows a delay for every single trip, with a median of 19 minutes and a range from 5 minutes to 1 hr 33 minutes (although the latter is an outlier).
I ran the same query for October–December 2017, which again returns delays for every single trip, but within the range of 3 to 42 minutes, with a median delay of 14 minutes. The longest delays did not occur on the Thanksgiving holiday, as I might have expected.
Another resource is provided by DixieLand Software, which provides status maps based on information posted to Amtrak's website. You can look up the Northeast Corridor map to see its status, or find historical train status by service name and train number.
Given this, the train arriving 13:22 is a safer option than the train arriving 14:22, especially if you have heavy bags. You may be able to get something arriving in between on SEPTA and NJ Transit, but these trains are commuter-oriented and so make are slower and make more stops, and require a transfer in Trenton, and when there is congestion, the Amtrak trains have priority.