I would smoke the pale instead of the Vienna. This will give you a better smoke flavor and avoid any chance at picking up acrid or astringent smoke flavors. If you want a very smoky beer, I would smoke both the Vienna and the pale. 15 minutes would probably give you something a little less than a Rauch bier but with some full flavored smoke to it.
Just remember to use a spray bottle to moisten the grain when you stir. The small amount of moisture prevents scorching and yields a smoother smoke flavor.
Good luck and let us know how it turns out!
