There are very frequent FPS drops on a local server with 10/16 GB of RAM on a dedicated server, not only for me but also for my friends on their personal builds (https://steamcommunity.com/sharedfiles/filedetails/?id=3577134028)

Are there any ways to optimize it?

AMD Ryzen 5 2600 Six-Core Processor 3.40 GHz
RAM 16,0 ГБ
Videocard Radeon RX 570 Series (4 GB)

Hey, just few questions if I can. Do you have Mount crow mod? First suggestion, have you increased local ram use for PZ? which is by default 1gig.
This guide here can help with that. I recommend 8g, specially if playing in Mount crow, it is very detailed and can slow down some PC. Also local online with 10gigs is fairly low.

https://www.reddit.com/r/projectzomboid/comments/spsq6c/tutorial_to_allocate_more_ram_to_finally_play/