Fix iOS Slow On Old Device
Most of the iOS users would get a speed improvement on their iPhone iPad. But some old device owners, including iPhone 6 and iPhone 5s users, are suggested not to install this iOS 12/12.1 update since they may get a slow iPhone iPad after the updating. Of course, after updating, people can downgrade to previous iOS 11.4.1. But Apple will stop signing iOS 11.4, iOS 11.4.1 after a week, so you may not go back to iOS 11.4 after you found your iOS is so slow.
Surely, there are some tips to temperately speed up your slow iPhone:
*Offload Unused Apps
*Clear App Cache and Data
*Free up storage of your iPhone iPad
*Turn Off Unnecessary Features on Settings like background app refresh and automatic app downloading.