Wow, I wonder if the 95% of reddit users for your sub that use the new format are net new to the site, or if there actually are a lot of old-reddit users that happily converted to the new UI.
Don't get me wrong, the old UI was awful, but it was much more information-dense, so I prefer it. I think it's unlikely that anyone that's not already a turbo-nerd would come as a completely new Reddit user, compare the two, and pick the old UI.