In a terminal server session (RDP / RDS) Outlook, or the whole Office 2013 suite seems very slow in comparison with Office 2010.
To workaround this issue you have to change your RDP-Display options to 16 or 24 bit (32bit is default).
To do this:
Open ‘remote desktop connection'(mstsc)
Choose ‘Show options’ -> Display -> and at Colors Choose ‘High Color 16bit’ or ‘True Color 24bit’.
Reconnect to your sessions and Office 2013 should be a lot faster.