You're running an 20 players mc server with that hardware? How? In my experience Minecraft-servers are insanely resource hungry, especially whilst generating new parts of the map or larger red stone contraptions. Back when I played around with hosting servers I used the "most optimized" mc-server fork called Tuinity - and even with that I had to allocate way more cpu and ram to the vms then u use. Would love to hear about your setup.