After the initial load your site performed fine. That leads me to believe you have some Pepper installed which is doing ip-based tracking (location lookup?) that occurs once and is somehow bogging things down. I see you have XXX Strong Mint installed. I know that’s been known to cause problems with Mint 2, especially with Secret Crush installed (which I see you have). I would try removing it and seeing if load times improve.
Other than that, I would just try general things. Ensure you ran ?moved after the update. Make sure your database doesn’t have an insane overhead by checking it out in phpMyAdmin (and running a repair if it’s out of the ordinary). There are a couple of other errors on your site (such as Last.fm plugin throwing back errors). Double-check that some other problem isn’t somehow related to Mint (I doubt it, but it can’t hurt).
Hopefully one of my suggestions clears things up for you.