iPhone SE MLXM2X/A - Unwanted upgrades
I have an old trusted SE which I use daily not as a phone but as an audio player. On it are some audiobooks in .aax format from the very well known distributor. There is NO sim card, only occasionally I switch on access to my home net via WiFi. The crutch of this tale is the latest upgrade that Apple would upgrade ios 15.7.9 at 2.9 Gb, this machine is only 16 Gb TOTAL. This machine is running at about 14.9 Gb. I don't want an upgrade my needs are simply to listen to a .aax file each day, no chats, calls, calendar, etc . So please you knowledgeable folk out there, would you please advise me as to how to keep my little "Audiobook" running. My thanks, Dave
iPhone SE, iOS 14