Eve Online probably wins the slowest tickrate award with its whopping 1 tick per second.

IIRC it gets even slower during massive battles where there are hundreds/thousands of players on the same server and area

https://wiki.eveuniversity.org/Time_dilation

I thought EVE was (near?-)tickless but with all interaction subject to substantial cool down timers that limit input frequency into the core?

Yup. As a plugin dev it has its weird quirks but it's quite amazing how the entire time runs at that speed