Preview at WWDC likely in June, followed by September launch.
Apple Seeds First iOS 9.3.2 Beta to Public Beta Testers
Beta testers who have signed up for Apple's beta testing program will receive the iOS 9.3.2 update over-the-air after installing the proper certificate on their iOS device.
Those who want to be a part of Apple's beta testing program can sign up to participate through the beta testing website, which gives users access to both iOS and OS X betas.
iOS 9.3.2, as a minor 9.x.x update, focuses primarily on performance improvements and under-the-hood bug fixes to address issues that have been discovered since the release of iOS 9.3. We don't know all of the fixes that will be included, but one issue with lagginess when activating Quick Actions in landscape mode on an iPhone 6s has been fixed.
No other outward-facing changes or immediately apparent bug fixes were discovered in the first beta of iOS 9.3.2.