It is so normal if you have been faced any problems with the Bluetooth connectivities on iPhone 6S. What should do to solve the issue if Bluetooth does not work properly in iOS 9? look at our following solution.

 My case was I could not connect my iPhone 6s to the bluetooth device in my car. Your case might be different. Whatever it is, take the following steps to solve your own issues:

• You should attempt to reset your iPhone 6S first. Press and Hold the Home and Power buttons together to turn it off, then turn it on.
• Toggle Bluetooth ON then OFF (go to Settings →  Bluetooth → on/off)

• Still not work? Reset the Network Settings

Go to Settings → General → Scroll down and select Reset → Reset Network Settings.

• Particularly, in the case your iPhone 6S still recognize the bluetooth device, but they can not connect to each others, you can attempt “Forget Device” solution.

From Settings → Select Bluetooth → tab on “i” next to the device name → Forget Device.

After removing the device from the list, you can attempt to reconnect again.

• If all above does not help to solve the problem, Do DFU Restore:

1. Get DFU status
You need to get your iOS device to DFU status by holding the 2 buttons (Power and Home) in 10 seconds roughly. And then free the Power button and keep holding Home button until iTunes get connected to your iPhone.2. Press and hold Option + Alt on Mac keyboard or Shift in Windows and choose Restore iPhone3. Select setup as a new phone.

Hopefully, my solutions would help.