This is according to data from Mixpanel in which they discovered that as of the 20th of December, 65.3% of devices were running on iOS 15. This sounds a lot compared to Android, but when you compare it to iOS 14, within roughly the same timeframe, iOS 14 was installed on 80.9% of iPhones.
What’s interesting and a bit odd about this is that for the past three iOS updates, Apple has not dropped older iPhones from the support list. This means that dating back to iOS 13, devices like the iPhone 6s have been supported until now, which means that even more users should be rushing to install the latest update.
However, it is possible that over the years with various bugs spotted in the early releases of updates, iOS users have grown more cautious over time and have held back from rushing to update the moment it is released. 65% is still very respectable in the given timeframe, but definitely not what it used to be, but more than likely we expect to see those numbers rise as we move into 2022.