I understand that the Under has covered in 17 of the first 20 preseason games going into today. But a lot would have to go right for this total to stay Under considering how low it is.

The Jets and Packers have been scrimmaging against each other. The Jets' ground game has looked decent. Some of that has to do with the Packers missing their two best run defending linemen. This isn't going to change, though, because the Packers are going to play backups in this game. 

The Jets have to get their passing game working. So they should be airing the ball out. Zach Wilson should see action. The Jets can risk that knowing the Packers won't be using their defensive starters. Wilson has to get some real game experience. Wilson has multiple decent receivers.
The Packers, too, have outstanding receiver depth. The Jets have arguably the worst cornerback depth in the NFL. 

Third-stringer Kurt Benkert is likely to play most of the game for Green Bay. He has a gunslinger mentality rather than a checkdown mindset. Benkert was close to the late Greg Knapp, the long-time QB coach who recently died in a cycling accident. Benkert got to know Knapp when they both were with the Falcons. It wouldn't surprise me to see Benkert play well in this dedication game to Knapp.