How do I sync my iPhone and 2015 MacBook
To Sync your iPhone via WiFi your iPhone needs to be connected with a cable to the MacBook once. Then in iTunes there will be an option on the main screen for the iPhone where you can select "WiFi Synchronization". 

This will make it possible for the iPhone to be synced when on the same network and manually when navigating to Settings > General > Wi-Fi iTunes Synchronization.