I have been looking into this same issue for my Yerf 3202. It seems that the 15 6 6 is the tallest tire for those rims. Does your model have adjustable shocks? You can use that to pick the front up if you are just after ride height. When it comes time for rear tires, there are 20" options, and even 20x10-8 tires so you could go taller and widea in the same style turf tire.
I have been wondering how something like these would help... You could then bolt those on and then an atv or golf cart type rim tire combo.
Not sure how the ride would be, turning, and street on tie rods would be. People commonly get those on the 150cc yerf that has a rack & pinion - and have had good results.