Usually the limiting factor is the disk speed of the database server, as well as the web server. What type of disks are you providing to these VM's?
disk is a vdisk and behind is a big FalconStore Machine with a HDS Datastorage. (No SSD Cache)
Yout think really this machine makes so many iops?
With the specs you mention I would speculate the bottleneck is either the IOPS of the drive that has the database, or your MSSQL install depending on which version you are using. Performance for the web console is nearly linear based on how quick SQL returns the query results to Tomcat assuming Tomcat has the CPU cycles to send the pages.
The numbers you stated seem very bad, have you checked windows event logs for any error's on the hardware also?
We have speed problem on 6.0 and 6.1 when we activate french translation ? Maybe your web interface is not in english ?