iOS 15, iPadOS 15, watchOS 8 and macOS Monterey: Release date and eligible devices.

Apple unveiled previews of the latest software updates for their operating systems at the annual Worldwide Developers Conference. The updates OS are iOS 15, iPadOS 15, watchOS 8 and macOS Monterey.

Release date
The developer beta of all the updates are available to Apple Developer Program members at developer.apple.com starting today. A public beta will be available to users next month at beta.apple.com. The OS updates will be available as a free software update later this year, which is normally around September.

Eligibility.
iOS 15.
Here’s the list of devices that will be receiving the iOS 15 update:

iPhone 13
iPhone 13 mini
iPhone 13 Pro
iPhone 13 Pro Max
iPhone 12
iPhone 12 mini
iPhone 12 Pro
iPhone 12 Pro Max
iPhone 11
iPhone 11 Pro
iPhone 11 Pro Max
iPhone XS
iPhone XS Max
iPhone XR
iPhone X
iPhone 8
iPhone 8 Plus
iPhone 7
iPhone 7 Plus
iPhone 6s
iPhone 6s Plus
iPhone SE (1st generation)
iPhone SE (2nd generation)
iPod touch (7th generation)

iPadOS 15 is compatible with these devices:

iPad Pro 12.9-inch (5th generation)
iPad Pro 11-inch (3rd generation)
iPad Pro 12.9-inch (4th generation)
iPad Pro 11-inch (2nd generation)
iPad Pro 12.9-inch (3rd generation)
iPad Pro 11-inch (1st generation)
iPad Pro 12.9-inch (2nd generation)
iPad Pro 12.9-inch (1st generation)
iPad Pro 10.5-inch
iPad Pro 9.7-inch
iPad (9th generation)
iPad (8th generation)
iPad (7th generation)
iPad (6th generation)
iPad (5th generation)
iPad mini (6th generation)
iPad mini (5th generation)
iPad mini 4
iPad Air (4th generation)
iPad Air (3rd generation)
iPad Air 2

watchOS 8 Compatibility
watchOS 8 requires iPhone 6s or later with iOS 14 or later and one of the following Apple Watch models:

Apple Watch Series 3
Apple Watch Series 4
Apple Watch Series 5
Apple Watch SE
Apple Watch Series 6
Apple Watch Series 7

macOS Monterey is compatible with these Macs:

iMac Late 2015 and later
Mac Pro Late 2013 and later
iMac Pro 2017 and later
Mac mini Late 2014 and later
MacBook Air Early 2015 and later
MacBook Early 2016 and later
MacBook Pro Early 2015 and later

The lists clearly shows Apple’s commitment to supporting older devices with the latest software for up to 6 years or more like the iPhone 6s series which was launched back in 2015 and the Mac Pro from late 2013.