Here's how you can fix slow performance issue on iOS 9 using the following workarounds.
iOS 9 is packed to the gills with a ton of new features, but along with the host of changes come the obvious performance related issues on certain hardware, especially older ones. If you feel that your device is giving up the ghost on you then you might want to try the following fixes to get some performance back while also saving battery life during the process.
Turn Off Motion & Fitness
If you're not using motion and fitness tracking features on your iPhone or iPad, then you might want to turn the feature off to regain some performance.
1. Open the Settings app and then tap on Privacy.
2. Now tap on the 'Motion & Fitness' entry and turn the 'Fitness Tracking' toggle to the OFF position.
Reduce Motion
Turning off parallax effects in iOS 9 really helps a lot.
1. Launch the Settings app then tap on General.
2. Now tap on 'Accessibility.'
3. Find the entry labelled 'Reduce Motion.' In here, turn the 'Reduce Motion' toggle to the ON position.
Turn Off Siri Suggestions
If you're not taken by Siri's new suggestions feature, then you might want to turn it off altogether.
1. Launch the Settings app then tap on General.
2. Now tap on 'Spotlight Search' and turn the 'Siri Suggestions' toggle switch to the OFF position.
Turn Off Background App Refresh
Apps refreshing in the background can take a massive toll on the overall performance of your device.
1. Launch the Settings app and then tap on the General entry.
2. Now tap on 'Background App Refresh' and turn the feature off.
Avoid Using A Dynamic Wallpaper
While Dynamic Wallpapers look good and all, but they can reduce performance of the device in a massive way.
1. Go to the Settings app and then tap on Wallpaper.
2. Over here select a Still wallpaper instead of a Dynamic one.
Turn Off Unnecessary Notifications
Unnecessary push notifications also take a huge toll on performance and battery life as well. Turning off unneeded notifications is the way to go here.
1. Launch the Settings app and then tap on Notifications.
2. Under the 'Notification Style' section tap on any entry you wish to not receive a notification for and move the 'Allow Notifications' toggle switch to the OFF position.
Restore Fresh
Going through the OTA route to update to a new version of iOS can cause a bit of problems. If the above mentioned fixes didn't work for you, then you might want to restore your device from scratch using iTunes. Follow our guide posted here for complete details on how to do just that: How To Download / Install iOS 9 On iPhone, iPad, iPod touch The Right Way.