The Newark parking situation has gotten quite a bit worse since before covid, and has even gotten worse over the last few months. That $15 rate you were quoted seems to be the new normal, at least for dedicated parking lots. My favorite Newark lot (Park Plus) seems to have closed at some point during the pandemic. I tried Value Parking back in April and was pretty satisfied with them, but their rates seem to have gone in that time from ~$9 to $15 and they're now closed between 1 a.m. and 4 a.m. The hotel lots can still offer better deals -- Park Plus has the Renaissance hotel for $7 plus BS fees, but, as craz notes, their shuttles tend to run less frequently and they drop you at the AirTrain instead of at the terminals.