Update question

Yes, that is included in iOS16 -- see the information in Unsend and edit messages on iPhone - Apple Support including the following:

Note: To unsend or edit text messages, you must be using iMessage with iOS 16 or later. If your recipients have devices with earlier versions of iOS, they receive follow-up messages with the preface “Edited to” and your new message in quotation marks. SMS messages can’t be unsent or edited.

You should be able to upgrade to iOS 16. I have seen other reports here of people who upgraded to 15.7 having difficulty upgrading to 16 but don't know how or if that was resolved. You may want to contact Apple -- there is a Get Support link at the top right of this page.