The left nav will be coming to all sites, including this one, over the coming weeks, as discussed in this meta post which has been featured on the sidebar for a few weeks. It'll probably be July or beyond before it comes to RPi... but it will eventually.
The interesting sort hasn't changed. Stack Overflow has used the 'interesting' sort for years, because the 'new' sort is just too noisy to be any use. On other sites, the sorting order will remain as it is (you can see Meta.SE as an example of a site that doesn't have the 'interesting' sort but does have the redesign).
I'm guessing you use the /questions page, which gives you a preview of the post's first few lines. That still exists in the redesign; you just click 'Questions' in the left bar instead of the top instead.
When the upgrade does finally come, you won't be able to retain the existing format, but you can hide the left navigation with a profile setting. It would then look like this. That does make it harder to get to the /questions page though, so probably wouldn't be very convenient for your workflow.