Your experience isn't typical, I'd hazard.
In a 3 hour session in store of D&D 5E, I've routinely gotten through 3-4 encounters of "average" difficulty.
Sentinel Comics it's more like 2-3 encounters of "average" difficulty
In a 5 hour session of AD&D 2E, in store, I would struggle to get through the Retail Play modules with 5-10 encounters.
In my home games, AD&D combats typically took 30 minutes to an hour. Cyclopedia, 20 to 40 minutes. 5E varied from 10 minutes to an hour, save for double-deadly which ran up to two hours.
My SG1 game via discord had several hour to 1.5 hour fights, but that was because of careful use of terrain and the slowdown of VOIP gaming with a VTT, and two players severely prone to analysis paralysis.