Probably not. As warned in the change log (and the change log of the beta released a month ago), the 1.5 patch is big enough to break saved games. Steam unfortunately has no easy way to revert to old versions.
While this is true, there is some hope moving forward. You can choose to install future patches to your games manually when they come out, just as an FYI. This is an option in Steam itself which can help prevent some of the 'save-game' headaches.
If you have any questions or concerns please let us know and we can get a quick 'How-To' setup to show you.