Hey Zombi3,
Do you remember if you were playing on the regular NS2 server or the new one?
IP for the "old" server: 66.151.138.182:27085
If you were playing on that server, then yes, we're aware server tickrate drops considerably with 20 players, especially after a long round when lots of entities are spawned. It does affect players performance, and that's why we opened a new server weeks ago. Here's the new server's IP: 74.91.118.234:27015
Now, you mentioned lag. All our servers are hosted by NFO out of San Jose, CA. You can read more about their network here:
https://www.nfoservers.com/networklocations.php Ping depends on location and connection speed obviously, but overall we're pretty happy so far. We usually get ping complaints during DDoS'd, which are unfortunately frequent, though they are taken care of within 5-15min maximum. There were no DDoS's reported this morning when you played though.
I hope I answered your post a little bit, but if you're still seeing bad ping/performance issues on our new NS2 server, feel free to post back here or contact me via PM directly.