I have an older device. I had to delete all the apps, all the data and even then my iOS update failed due to lack of space. It’s only when I cleared the OS cach

I have an older device. I had to delete all the apps, all the data and even then my iOS update failed due to lack of space. It’s only when I cleared the OS cache by doing a factory reset that I was able to update to iOS 15. This device was a spare I just use for reading ebooks but I imagine if it were my primary phone I would balk at deleting everything just to update the OS.