Outlook 2010 and Outlook 2013 by default displays animation while expanding message conversations or Groups. If you are not interested in animation effect and want to reduce time to expand the groups and conversations then you can use the settings available as part Outlook options.
Step 1: Click File menu and select Options from the list.
Step 2: In the Outlook Options window, click the Advanced options.
Step 3: Scroll down to Other section in Advanced Options screen.
Step 4: Un mark the checkbox with label as Use animations when expanding conversations and groups. Click OK button to confirm and save the changes. This should expand the groups and message conversations quickly.