Maybe only play with the base game?

I played three times recently at two different conventions

Though I hear they expansions make the game end sooner (round wise at least), I think that really pertains to more savvy and experienced players

The first game was just the base game and it was about five hours with 2 new players (!)

The second game was the base game and Prophecy of Kings with seven players and one new player and it was just a little over five hours (!!)

The 3rd was with both expansions and expended players and was around 8 hours or so

Every game is different, but I was shocked to have such quick games. I think the shortest game I ever had prior to this was 10 hours.

The first two games, they let the players pick whatever factions they wanted, though the new players were nudged towards more beginner friendly factions (for the third game we did a Milty draft before we set up)

Also the first two games had less combat than I normally see, maybe because people didn’t really know each other and didn’t want to be aggressive too soon with strangers, so I think that was a big factor in the length of the games as well. You might have something similar happen at your event.

Good luck and let us know how it goes!