I'm not really 100% sure if the plug-ins have anything to do with the lag. I'm not exactly an expert in this field so I can't really give my opinion.
The lag isn't coming from the plugins. The server has enough megabytes. The lag is coming from machines/farms and dropped items mostly. Also it happens to occurs when there are a lot of players at the same spot.
Possible causes for lag right now: Specific plugins generating errors or impacting on server load Entity lag by large farms with hundreds of spawners but the most significant issue that is most likely causing the lag is the server itself. At any given time the plugins we have wouldn't lag a server. The world file contains over 600k islands. It is so large in size. The server hasn't been reset since it opened (at least if it had, its been up since 2012). The age of the server is starting to show.