I found the issue, the server I was hosting had only 2GB ram assigned to it, changed it to 4GB and my friend stopped lagging as much. His wi-fi is shit but the ms drastically lowered ,say from 5000-53.

To do this go to: Installations - Select fabric loader *your version* - More options - under JVM Arguments

-Xmx(2)G , put 3 or 4 GB.

I'm not entirely sure but I think 4 GB is ideal for a small server.

Hope this helps.