@edbpcc To reduce the size of the video you will reduce the quality when you lower the video resolution. One option, you can download the video manually and use an online converter. Then replace the video in Stream.
I highly suggest you manually download the video from Stream and upload it in OneDrive or SharePoint. Then you can use the "Send a link" feature to properly share the video without attaching to the case system. This will get you around the minimal file size requirement in your case management system and also provide a way for users to access the video link in a consistent manner. This will also allow the video owner to update the video and not having to update it in multiple locations.