As @poongarg suggested, make sure you're meeting the VM spec - but I guess you would have experienced an overall slowness of the system if you had grossly underspec'd (e.g. 8GB instead of 16GB)
I have noticed that the web interface code may have something to do with it - and if my ISE page freezes (with the correct VM spec! or on SNS appliance), then I press CRTL-F5 to force a reload. This is quite common with Cisco web interfaces - in my opinion most are not optimally designed. The worst offender is the Cisco AireOS WLC interface - no matter which browser you use, it will suddenly stop working (no more changes can be saved) and you have to shut the browser down and start again. Sometimes the login doesn't even work. I have heard of folks having to use Incognito mode to work effectively in DNAC (the latest generation of Cisco GUI technology) because it's also flakey.
It's not the browser's fault. Never happens with my VMWare vCenter GUI - rock solid and gives application-like experience - it's so well designed that you forget that you're working in a browser.
