I was always bothered by slow performance of my lab installation of vSphere Web Client (version 5.5). Although my lab is small I have large number of plugins. I use the Windows installable version which is running together with vCenter, Inventory service, Update Manager and database server.
I noticed that the Java process was using over 1 GB of RAM. The fix was simple – add more memory to the VM and to Web Client Tomcat server:
Edit wrapper.conf file which is located in C:\Program Files\VMware\Infrastructure\vSphereWebClient\server\bin\service\conf.
in the JVM Memory section. I increased the value to 3072m.