slow loading people's canlendar in Outlook 2010 client scheduling assistants?

it always takes one mintue to get one people's calendar updated from MS outlook 2010 client.

However from OWA web app, i added the mail web site to the trusted web sites of IE, the loading is almost instant - guess this is good enough!

Any ideas why the client is so slow? also slow to find rooms and suggested times.

Seems the client not configured to do the right request through network.

Thanks,