iOS 16 adoption rate is quite good ahead of the announcement of iOS 17
Across all active iPhones (including any models), 81% are running iOS 16, 13% are running iOS 15, and just 6% are running unspecified earlier versions of Apple’s mobile OS.
Meanwhile, 90% of the newer iPhones (introduced within the past four years) sport iOS 16 as of June 1. There are still 8% of these newer phones running iOS 15, and just 2% run an older, unspecified iOS version.

However, that shouldn’t really surprise you – usually, Apple has wider adoption of its newest iOS when compared to Android (just think that Android phones come from many manufacturers, while iOS is only available for iPhones).
On the iPad front, things are also brighter for iPadOS 16. According to Apple’s stats, adoption of iPadOS 16 has increased notably and now 71% of all active iPads are running it (in February, this figure was 50%).
As for iPads released in the last four years, 76% of them are sporting iPadOS 16. 18% still run on iPadOS 15, and 6% use an older version of the OS.