I’m personally of the opinion that you should keep Chapter 12, and cut Chapter 15. Cara and Greef are two of the main characters of your Season 1 edit, so their return would be satisfying for the audience. On the other hand, Mayfeld’s episode was cut from your edit, so he would just be some random guy that Mando knows for some reason. We already have two instances of characters who were cut earlier being reintroduced with no explanation, so if we had to add one more I would prefer the Mythrol rather than Mayfeld. The Mythrol’s role in Chapter 12 was small, so he could just be some random comic relief guy.

Also, I have a strong feeling those clone tanks are going to become important later. The Dark Troopers have already been confirmed to be droids, so it obviously has no relation to that. Whether it’s related to Palpatine or not (and I suspect it is), we know it’s going to be important. So I would rather keep that important bit of foreshadowing instead of an episode with nothing really critical to the story.

EDIT: And one more thing I forgot, if you cut Chapter 12 you lose Mando finding out that Gideon is alive. It’s a crucial element of the story, since Mando was sure he was dead previously. If you cut that, it creates a plot hole.