It might be a little too optimistic, given we don't really have a workhorse running back for the goal line. We also can't expect Griffin to duplicate the 14 rush TDs Newton had, which IMO is the only way the team would be able to close in on 20 rush TDs.
Twenty pass TDs is definitely reasonable, though. Maybe 20 pass, 12-15 rush. Put us in the middle of the pack in the NFL.