[M. Bison]

I'm not sure what's wrong. I've restarted the servers multiple times and this has only resulted in the issue temporarily subsiding. The next day it spontaneously reoccurs and persists until restart. The cpu usage of each server when entirely full generally spikes no further than 50-60% on a single core. The last few days it's been idling at 100% even when there's less than 15 players. I suspect a broken addon or plugin may be at fault, but there's always the chance the servers are under some kind of attack.  :o

It did become playable now

That's because I restarted it.  :-\

it's very obvious that when office server gets overloaded with 250 pingers it starts laggig.

nonsense.

Even my own ping goes from regular 30 to 120-150.

This actually sounds like your connection isn't able to maintain the minrate of the server. If you can't sustain a downstream of 51KB/s during sporadic bursts of traffic, then you'll likely experience a spike in your ping.