I have turned off the preview when I hover over any items in my task bar. On my main task bar the preview no longer shows up, however on the Dual Monitor Taskbar the preview still shows up after 2 seconds.
This is where the variable is turned off:
Click on Start button and type GPEdit.msc in Instant Search text box, then hit Enter.
Navigate to User Configuration > Administrative Templates > Start Menu and Taskbar in left pane of Local Group Policy Editor.
Locate and double click on Turn off taskbar thumbnails in right pane of Local Group Policy editor.
Select Enabled radio button.
Click OK to make the change effective.