v.143 - RED: First Impact Update Notes - Part 2

The fact that they won't be updating every second * how many npcs update every second * how many towns they're in should help make the entire server less laggy. They'll just be updating every second * how many npcs update every second.

"Town lag" isn't server lag, it's client lag.
Your client is going over those NPC's scripts trying to decide which animation to show, over and over.
A room with all of them is just as laggy as a whole town (the room in Aquarium which had them is both example and proof: that small room is laggy, the big town outside is not).