I have the same issue as Adafruit nrf52 core users experienced before: intellisence doesn't recognize Arduino code when nrf5 boards are selected 
Avr and esp8266 boards work fine. 
I am using the latest VM release and VS2015

Sorry for the delay. I will look into it but you can add it yourself...

Use the option to create a "local board.txt" in the project folder or add one yourself.

Add one property to it:-

intellisense.include.paths={runtime.hardware.path} 

Click "save" after changing the board.txt because when you build VS saves the file after the build. Can be confusing.

After changing the file a build will force the change to be recognized immediately. VS will detect the change and that status bar should show intellisense is updating in the background. When that finishes your intellisense should work?

EDIT: The next release 1709.03 contains this change as standard but I'll leave this post here because it's useful for people to know that intellisense paths can be extended with a semi-colon list of intellisense.include.paths=