go to your server properties file and you will see a bunch of optione if you see player slots only do 5 instead of 20. (and i recommend only 5 plugins)
if you are trying to host it on your pc give i recommend you to put it at 12 player slots and 10 plugin slots for every giga bite you gave your server, also use ngrok, and also use the commmand /butcher to kill all the lag, and make sure to have essentails installed it really does the job well!