so, IIUC, you moved from a physical machine to a VM, and from 4GB of ram to 2GB..
well, it seems to me you are understimating the thing.. your server (the old one) had all resources dedicated to its tasks..
now you have a VM (which can not challenge with a real one) running on a host where other VMs are running (and so you forgot to consider I/O disk matter) and powered by an atom CPU.. I hope that, at least, NS VM is using a dedicated network interface..
if you really want to make some king of comparison that makes sense, give at least the same ram amount to NS, but IMVHO your hw is not made to run 3 VMs
BTW, how did you manage in getting 8TB of storage with 2 hds?