Modifying memory usage on server?

Hello,

I have a rust server with an average of 150 player, but when it its the top the server starts dropping the fps, I sow in the machine that half the core and only about 6 gb of ram whasin use (of 16).

So my question is, how do I change the ram usage for the server?

Here are the spect of my server:

RAM: 16GB
CPU: 4 core
SSD: 110GB

 

Thanks in advance for the help!

If the server does not use more ram means it doesn't need more.