Do you see the same difference running Pega's MySupportPortal in IE versus Chrome? If not, then we're looking at something in your application that may need fine tuning. This may need an SR to dig deeper.
The next step I would take would be to try and pinpoint the bottleneck. Sometimes, a Fiddler trace will show you where time is being consumed. For example, attached is a Fiddler screenshot showing activity when I refreshed Designer Studio from Chrome.
You can compare sessions from two different browsers and see if you can pinpoint an issue.