Lag on Paper 1.15.1 despite OK TPS

Hey guys,
I have a Paper survival server we play on, and for the players other than me (I’m the host), the server is quite laggy and they often get kicked because of timing out. I’m not an expert in this field so I need help to figure out why this happens. My connection should fine (~20-22 Mb/s upload speed) and theirs, too.

I use a Ryzen 5 3600 to run the server and I gave it a max of 12GB memory (it never uses as much though, just in case) out of 16.

Here is a timing graph:

Thanks in advance for the answers.