There’s a tram line in Dublin which hits every three minutes at peak times, which is just bonkers (it’s not fully segregated, so if there’s any traffic problem at all then about four of them end up piled up one behind the other). Its most busy section was meant to be converted to metro, but due to planning permission nonsense it will just continue to be one of the world’s busiest tram lines until at least 2040 (it is actually higher peak time capacity than many metro lines at this point).

They just got permission to go from 22 to 26 trams per hour at peak times. I’m thinking that by the time it gets metro-ified it’ll just be a continuous procession.

Trams running every two to three minutes on a few central sections is nothing out of the ordinary in a number of tram systems.

The Victoria Line in London has a 100 second interval, although apparently in practise it's more frequent: https://www.youtube.com/watch?v=PJ0zk4MWCQY

From a quick search, there are also lines in Paris and Moscow with similar frequency.