Apple iOS 18.3 New iPhone Software: Should You Upgrade?
Apple iOS 18.3 is compatible with all iPhones that can run iOS 18. This means all iPhones from the iPhone XS onwards, including the second- and third-generation iPhone SE models.
Business Insider India4y
Apple's iOS 15 may not support for older devices like iPhone 6, iPhone 6s plus and iPhone SE
iOS 15 will run on the iPhone 7, iPhone 7 Plus, and all newer iPhones that have been released, making it compatible with devices that have an A10 chip or newer.