Most of the iOS 9 problems like stuck on Apple logo, stuck on iTunes logo, iPhone won't boot issues can be solved by force rebooting or restoring your device:

Step 1. Hold and Press Home & Power button for 10 seconds to reboot your iPhone. If it still stuck on Apple logo, you will need to put it in recovery mode.

Step 2. Plug the iPhone to your computer via the USB cable and make sure that the latest iTunes is installed.

Step 3. Press and hold Home & Power button for 10 seconds. Then release the power button but keep pressing the home button.

Step 4. You will see the Connect to iTunes screen and you can let go of the Home button.

Step 5. Now you can restore your iPhone with iTunes.