With Spigot, it is possible to pin-point potential causes of lag on your server by using the Spigot Timings feature.
To use the timings function, simply type the following into your server console:
After that's done, you should be given a URL in the console window that would show you your timing results. It is parsed into a way that it easily readable and should give you a pretty good idea of where your lag is coming from.
For other lag troubleshooting methods, check out our other guide: