An easy way to speed up the display of the Start Menu Items is to turn off the menu shadow.
Right click on an open area of the Desktop and Select Properties
Click on the Appearance tab and Click on the Effects button
Uncheck Show shadows under menus and click ok two times
Using Registry Editor
Warning: Incorrectly editing the registry may severely damage your system. Before making changes to the registry, you should back up any valued data on your computer.
Start Registry Editor from start>rub type regedit and click ok
Navigate the HKEY_CURRENT_USER/Control Panel/Desktop/ key in the registry from your left pane,now you need to check “MenuShowDelay” value on the right pane and double click on that
Change the value 400 to 0 and click ok
Close the registry editor.