I have three virtual OES 11 SP3 servers that are hosted on the same hardware:

A Dell PE720 running dual E5-2770 cpu's with 128GB of RAM.
The host server is running vSphere 5.5.

Two of the servers host my institutions data storage; one for users' home folders and one for shared data.
The third server handles my GroupWise 2014R2 system's sole post office and its attendant secondary domain.

The two data storage servers are configured with 8GB of RAM and two vCPU's.
The mail servers is configured with 16GB of RAM and four vCPU's.

While I recognize that the mail server has a LOT more going on, the server's performance in virtually and type of access (ssh, GUI over RDP or vmware console) is abysmally slow.
I feel like it's running on an 8086.
The same goes for working in the Admin console.
Online access from the GW client is also slower than I think it should be.

All three VM's are set up in what I call a semi-virtualized fashion.

While the boot drive is a vmdk file, the data storage for all three servers are accessed with fiber channel HBA's that are set up in pass-through mode; vSphere doesn't see the LUNS attached to those HBA's, so the LUN's are formatted with NSS, not NSS running within VMDK files.

In addition to the three VM's mentioned, the Dell hosts four fully virtualized servers.
Performance on those servers is just fine.
The decent performance of all the other VM's leads me to rule out the hardware as a part of the problem.

The LUN used by the email server is on a separate SAN array, running 15K rpm SAS drives in a RAID10 configuration.

The root drive of the email server and the virtual drives of the other servers are on a SAN array using 7200 rpm SAS drives in a RAID6 configuration.
The data storage LUN's are also on the slower SAN array, but like the email server, the LUN's holding the data are accessed by HBA's in pass-through mode.

Any suggestions to speed up the server are welcome. I hate to revert back to a physical server, but it may be unavoidable.