Recommendation here... I think especially on shared hosting, sometimes the easiest way to update is to asterisks (*) your extensions in the main composer.json. I tried various other things, including the basics like disabling all extensions... I made sure all of the extensions I have installed have been updated for beta 15. I just couldn't get it to update from 14 to 15. The recommendation is to add that workaround to each release's instructions. 🙂
