Some people did experience slowdowns in Verdistis, but AFAIK that should be pretty much fixed in the latest game version.
Some re-release versions of the game may already be updated to the latest 1.0034A version, as shown in the bottom right corner of the main menu; if you have an earlier version, you should install the
patch. The DVD version is already updated, and the patch (designed for the CD version) should not be installed.