If your iPhone or iPad is running slow, check the network conditions. Many applications require an Internet connection for their content and other functions. Close an application that is not responding. Make sure you have enough storage space.
It prevents the device from getting too hot or too cold. The next thing you can try for a slow iPhone is to clear the cache. This will optimize the device's storage and free up space on it. For a consistent good experience, it would be best to get used to restarting the iPhone at least every few days.
Keep in mind that you need at least 6 GB of free space to update your operating system and approximately 2 GB of free space to take new pictures, download new apps, and use your phone to the fullest. Always delete apps and files that you no longer use, or move them to iCloud or to your computer to keep free space on your iPhone. iPhones running iOS 11 and later will give you personalized space-saving tips in the “Recommendations” section of the general settings. You can update the operating system directly from your iPhone or by connecting it to a computer.
If you connect your device to your computer, open Finder or iTunes, connect your phone, search for it and download and update any available updates. While the iPhone's low power mode can be useful for saving battery, it can also slow down the iPhone. Restoring your iPhone to its factory settings because it's slow should be your last resort, as it erases all the data from your iPhone. If your iPhone is properly charged, you must keep this feature turned off to keep the iPhone running at its usual speed without any power restriction forcing you to slow down.
In other words, a slow-running iPhone, especially a slow iPhone 6, is a known problem, which is due to Apple's own “performance management changes”. This continues to affect iPhone 6, 6S, SE and 7 models, as well as iPhone 8, X and XS models with iOS 12.1 or higher. About the iPhone 15 The iPhone 15 came in four different versions and was available to the public.