The speed does not seem to be a concern for iPhone 6S or iPhone 6S users, but the battery life is always an obvious problem. Look at our following suggestions to speed up iPhone 6S and improve it’s battery life by optimizing iOS 9 in details.
Too many functions in iOS 9 slow down your iPhone 6S and of course drains the out the battery steadily.
Apple does take care on their customers by providing iOS 9 with the most necessary features that nearly meet the entire demand of customers on average.
The point is on Particular user, some is needed and some should be disabled.
Optimize iOS 9 to speed up iPhone 6S and Improve battery life
There are some easy and visible ways we do not mention in this tutorial: Disable Location Service, Turn Off Bluetooth and Wi-Fi when not using,… etc.
Disable Background App Refresh
Background App Refresh is a useful feature. It enables applications renew itself constantly in order not to miss any notice to users. Although this feature is pretty cool, but pretty much consumes the battery and reduces the performance of the device.
– To disable this feature, you go to Settings> General> Background App Refresh.

Enable Reduce Motion
Reduce Motion Feature will disable the visual effects in the background and the user interface, including the effect icon. To activate this feature, go to Settings -> General -> Accessibility.

Disable Push Email Function
Like Background App Refresh, “Push Email” is one of the causes of “famous” affecting the battery life of the device. This feature constantly checks and displays a message about email status. Here we have 2 options: Push and Fetch option. Unlike Push, Fetch usually only inspect emails for a certain time, not often immediately as Push.
– To disable Push Email, go to Settings -> Mail, Contacts, Calendars -> Fetch New Data.
Disable App Store’s Automatic Downloads
App Store’s Automatic Downloads is a very useful feature for busy iOS users when there is no time to update applications manually. However, this feature actually reduce the battery life of the device and sometimes wasteful your mobile data as it will be regularly checked, automatically download and update the new version of the application from App Store whenever a internet connection is available. For the one who install too many Apps, especially games, that disable this function does help to either speed up iPhone 6S or improve iPhone 6S battery life.
Settings -> App and iTunes Stores.
Utilizing Low Power Mode Function
Enabling Low Power Mode will activated “Low Power” automatically when the iPhone 6S is down at 10% or 20% of the battery, according to Apple, if enabled this feature on iPhone battery life may be extended by 3 hours. To activate Low Power Mode, you go to Settings -> Battery.

Last Words
All mentioned above are all essential solutions. If you Google, there are too many other articles from other sources about SPEED UP IPHONE 6S and IMPROVE IPHONE 6S BATTERY. You may find some additional ways, but we assume they do not really help.
Thank you so much for reading my whole article!