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.
We faced lots of issues and bugs from our new updated iOS 9 Mobile devices. I made a small list of these issues and how to avoid them.
Battery Life. This is an issue that seems to re-occur with every iOS update. Even though the reasons for that can vary from one device to another, there are several useful tips for improving battery life that you should try.
Check which apps are wasting battery
Turn off unnecessary features
Low Power Mode
Frozen Home Screen, If you were using an app, then it froze, double tap your Home button, then swipe up and close the app. If that doesn’t work, try holding down the Sleep/Wake and Home button at the same time to restart your phone
Overheat, Some users reported that their devices are getting hot after IOS 9 update, this might relate to the battery overworking. Try to close all apps you don’t need, turn off your wifi or mobile data, and get a new cooling case -available for iPhone 5/5s or iPhone 6.
Speaker malfunction, A weird bug reported by some users that when the phone is paired with a Bluetooth device, the speaker drop any sound. If you face it, then you should turn off your Bluetooth.
High mobile data usage, IOS feature may eat your data to support tons of new features like WIFI-assist which automatically use your mobile data when Wi-Fi connectivity is poor or weak. You only have to disable that feature to retain your data.