Everyone is claiming my server lags

Well i was starting to open my server.
Total plugin is 19.
20 if include playrust.io
but everyone in server starts to claim it has extremely high lag in the server if over 20 person.
also i have 16GB ram. i7-4790K cpu as well.
SSD too. now can i set ram into this server by my own?
im using oxide and batch file.
any ways to solve this
[also i dont lag at all ]
[not even fooling me they are all claiming]