iOS 15 is beaten by its predecessor in terms of adoption to date
Apple launched iOS 15 and iPadOS 15 about 7 months ago as new software upgrades available to all their applicable mobile devices, even if they are nearly 6 years old in some cases. Despite this, it seems that not all of them have gone to the trouble of installing them quite yet.
The latest stats on this subject, released directly from the OEM as of January 11, 2022, show that 72% of all iPhones from the XS to the latest 13 series run iOS 15, whereas 67% of all iPads released in the same time-frame run iPadOS 15.
This sounds like a good rate of uptake, if less so when compared with the 81% rate for iOS 14 in January 2021. It also sounds worse for iPadOS 15 when one considers that 51% of all eligible tablets everywhere actually still run older software.
This seemingly reduced rate of acceptance year-on-year might be related to the fact Apple no longer restricts access to upgraded security patches to the latest firmware upgrades. However, it might also have something to do with resistance to new measures the OEM has sought to introduce as of late, most notably the controversial CSAM initiative the company has been obliged to walk back in recent history.