iOS 15.3 seeded to beta testers, WatchOS 8.4 beta goes to developers 
Apple just started seeding iOS 15.3 to public beta testers so if you have a beta tester or developer account, you can download it right away. WatchOS 8.4, on the other hand, is only available to developers for now.
Both firmware updates focus on improving system stability and clearing out some bugs from previous versions of the software. There are no apparent visual changes nor there are any new features of note.
Keep in mind that beta versions of a given software are not meant to be used on daily drivers as they may contain bugs.
Via
Tech News For Today 