Yep. I wouldn't be surprised at all to find that in real life HVAC accounts for half or more of the total consumption on a typical stop-n-go route.

and postal trucks don't even have HVAC. At least the ICE ones. They get a lowsy fan

Yeah that is a major perk of the new postal trucks both EV and ICE is that they will finally get Air conditioning and an adequate heating system. The LLV had no AC which led to many issues in hot climates, and the heater was not large enough to heat the cabin well with the window open all the time.

I just had to Google to see whether or not they even had doors.

At least in SoCal they (almost?) always leave the door completely open and they wear shorts, clearly because they don't have A/C.

In GA, it's the same. They usually wear shorts too. It's hot and humid so I don't blame them!