Not a direct answer to the above question but wanted to post related SFSpeechRecognition issues in hope it might help others searching for speech recognition related issues popping out in iOS 15.
In our case users started reporting that after upgrading to iOS/iPadOS 15 speech recognition stopped working in our app. It wasn't widespread but there was an increasing number of reports.
Turns out Siri and Keyboard dictation settings can affect SFSpeechRecognition and wether it can perform recognition requests or not. Through logging and analytics events we were able to figure out our users were getting kLSRErrorDomain 201. The error message was fortunately descriptive enough (Siri and Dictation are disabled) to point us to Siri and Dictation settings and the figuring out some of our users had them turned off. Turning either off fixed the issue.
Linking a related forum post: https://developer.apple.com/forums/thread/690976
Hopefully any of the above can help other struggling with speech recognition issues happening after iOS 15.