https://wccftech.com/download-apple-releases-beta-1-of-ios-15-3-and-ipados-15-3-to-developers/

Apple has seen fit to release the first beta of iSO 15.3 and iPadOS 15.3 to developers for testing purposes. The new beta arrives four days after the company saw fit to release iOS 15.2 to the general public. If you are a developer and want to check out the latest features for yourself, you can download the latest build from the Apple Developer Center. Scroll down to read more details on what is new and what you should expect with iOS 15.4.

If you are interested, you can download the latest iOS 15.2 and iPadOS 15.2 on your compatible iPhone and iPad models through the Apple Developer Center or via over the air. Make sure that you have installed the proper configuration profile from the Developer Center for your iPhone or iPad. Compared to iOS 15.2, iOS 15.3 will be a minor update.