How to permanently fix IntelliSense poor functioning on SSMS?
SSMS 2016 is available for free. It has much better IntelliSense than in previous versions. https://msdn.microsoft.com/en-us/library/mt238290.aspx I highly recommend upgrading.

Other reasons why you may be having problems, from personal experience:


Highly utilized server makes it take longer to work. I have personally seen it take 5 minutes on a really bogged down machine.
Local machines with low resources.
Incorrect query syntax. This can cause IntelliSense to not load anything because it can not tell what it is supposed to be doing.
Poor connection between local machine and server. We just moved locations at my job, with a slower connection, and my IntelliSense load times have drastically changed.