The point to consider is to check if those 2012 VMs used for any specific workload or application or traffic is routed via some specific application such pfsense. You may also want to check duplex settings of pNICs plus compare the network usage statistics inside guest OS (with resource monitor)
The VM's are on the same host and network. I did check the performance and the 2008r2's has 0% utilization before the tests. The network traffic flows the same path on both vm's.