When the battery in iOS 15 runs out faster after the update, here are some suggestions

If you recently updated to iOS 15 or iPadOS 15 and notice that your battery life has deteriorated, the first thing you should do is wait.

It may not sound like a solution, but following a significant software update, the freshly updated iOS/iPadOS will have to make system modifications, indexing, and other operations, which will consume more battery power. So be patient, especially if you recently upgraded your program.

This is just basic advise. You should always install the most recent software update.

You may check into the new iOS/iPadOS update menu on a regular basis by navigating to Settings - > General - > Software Update and tapping "Download and install" if new software is available. Always make a backup of your iPhone or iPad before upgrading. As soon as iOS 15 was released, its version 15.01 debuted a few days later (even 15.02). This is often used for bug corrections, and if a flaw is known to be causing battery issues, it will undoubtedly be addressed in such an update.

Upgrading or updating the applications on your device is beneficial for assuring compatibility with the current version of iOS/iPadOS and may involve the resolution of battery concerns.

Tap your Apple ID profile symbol in the upper right corner of the screen to open the App Store. To install available app updates, scroll down and select "Update All."

Go to Settings -> Battery to see which apps are draining your battery.

You could see one or two outliers, generally streaming films or games, and you might consider discontinuing them if you're not utilizing them.

You may also check the battery health of the smartphone; if it is less than 80%, it may be a good idea to replace the battery - albeit this has nothing to do with the iOS 15 upgrade.

Disabling Background App Refresh is a typical strategy for extending battery life, and most users will notice no difference in how their iPhone or iPad works.

Turn this off by going to Settings> General> Refresh Background Apps.

According to several users, Spotify in particular is aggressively consuming battery life in iOS 15, and deactivating Background App Refresh appears to be extremely beneficial. Spotify promises that this issue will be fixed in an upcoming software update, which is why it's critical to upgrade the app as soon as it becomes available.

Low Power Mode might help iPhone users get more out of their batteries. Only iPhone users have access to this Mode.

Low Power Mode may be activated by going to Settings > Battery > Low Power Mode > ON.

Through the Control Center, you may also enable Low Power Mode.

Lowering the brightness of your screen can help you preserve battery life on your iPhone or iPad by causing the device to consume less electricity.

Adjust the screen brightness with the slider in Settings > Display & Brightness.

The Control Center also allows you to change the brightness of the screen.

Location services are wonderful and vital for Maps apps, as well as online transportation and food delivery apps, but they are not required for many other apps. Because location usage consumes the battery, eliminating unnecessary location usage might assist. 

To disable the usage of location, go to Settings -> Privacy -> Location Services and select the app. Set access to the site to "never" or "ask next time."

A simple reboot will sometimes address the battery depletion problem, so it's worth a go.

To force a Face ID reboot on an iPhone or iPad, push the volume up button, then the volume down button, then the side/power button until you see the Apple logo, then release.

To reset an older iPhone or iPad with a physical home button, press and hold the power and home buttons simultaneously until you see the Apple logo on the screen.