Recently my little brother's server has been lagging quite a bit. It says it is almost 1600 ticks behind.
It is spigot 1.15.2 and has the following plugins: OpenInv, Supervanish, ultimate mob heads, one person sleep, and core protect.
The first two plugins are relatively small, so I don't think they are causing the issue, I think that the problem may be core protect.
If somebody can help me out it would be greatly appreciated. 
Edit: Removed Openinv and super vanish as they were deemed not necessary by my little brother.