What can I do to stop the Lollipop update prompts if I don't want to update my KitKat?
Go into your device Setting--> Apps--> All (tab)--> Open 'Motorola
Update Services' &amp; Disable it! 
If 'Disable' Option is not available
in your device then you will have to root your device and then
install SD Maid app, And grant that application root permission so
that you can freeze system apps. 
And I think so 2nd method will work 100%.