Some users of older iPhones refuse to install iOS upgrades because they mistakenly think these will reduce the performance of their handset. But tests comparing iOS 15 with various previous versions found no sign of Apple’s latest turning any model into a slug. Some of the devices actually ran faster with newer software.
And the same goes for battery life, in general. Most older iPhones have a longer battery life with iOS 15, though some do see a reduction.