Doug, your wheels are 15" x 6", but what is the tire size? On a 6" wide wheel, they might be relatively wide tires.
Since the trailer doesn't need huge tires, but wants large diameter, I would be looking for a tall and skinny tire. I remember that real (original, not Golf-based) Beetles used 15" wheels, so I did a quick search and found that they might have used 165R15 tires, which would likely be 165/78R15 or 165/82R15 in the current fuller specification schemes (the "standard" aspect ratio changed over the years).
I did another quick search for "165R15", and the first match was back to
Coker Tire! They come with wide or narrower whitewalls, have lots of load capacity for a 2000 lb (loaded) trailer, and use a 4" to 5.5" or 4" to 6" wide wheel (depending on the tire model)... so 5" is a decent width.
I didn't look into the 14" tire choices, and I don't know how easy it is to find 165/78R15 tires from normal (i.e. not retro specialists like Coker) suppliers, but there are some possibilities, anyway. The Kumho PowerStar 758 might still be available in 165/80R15, for instance.