The Israeli The Verifier reports this, which also correctly reported which iPhones would be supported by iOS 14 in June. Apple annually releases a major new version of iOS that is often no longer suitable for older devices.
In 2019, the iPhone 5S and iPhone 6 did not receive support for iOS 13, and the iPhone 6S and first SE were the oldest devices that remained supported. With the step to iOS 14, those devices also remained supported, but that will change with the arrival of iOS 15. The oldest iPhone that will get iOS 15, according to The Verifier, is the iPhone 7 from 2016.
The iPhone 6S and first SE both use the Apple A9 chip, which is also in the fifth-generation iPad from 2017. It is therefore likely that the iPad will not receive support for iPadOS 15. The iPad Air 2 is currently the oldest iPad supported by the latest iOS version – the tablet appeared in 2014.
iOS 15 and iPadOS 15 are expected in September 2021.