The default speed of the Start Menu is slow, but you can fix that by editing a Registry Key. Start->Run regedt32 and navigate to the following key:

HKEY_CURRENT_USER \ Control Panel \ Desktop \ MenuShowDelay

By default, the value is 400. Change this to a smaller value, such as 0, to speed it up.

If the speed of the Start Menu is slow, even after using the FAQ above, then you might try the following: Navigate to Display Properties> then Appearance then Effects and turn off the option titled Show menu shadow. You will get much better overall performance on your system.