How many are your SEP clients? Also what application or services are running on your VM host, because eventhough you are running on a VM guest and your server was properly size up, trafic was basically travelling on single network to your VM host that might cause bottleneck (as mentioned by SMLatCST).
In addition for you SEPM sizing:
The Shared Insight Cache Server runs on a dedicated server or virtual machine and requires the
following:
Windows Server 2008 32 or 64 bit, 64 bit is recommended for best performance
-30 GB of total disk space
-CPU requirements
For less than 100 clients a single core CPU is acceptable
For more than 100 clients two CPU cores are recommended
-RAM requirements are dependent on the number of clients in the environment
2 GB for less than 100 clients.
4 GB for 100-1000 clients.
8 GB for over 1000 clients.
Best Regards,