Actually.. I think it would be just the opposite affect. The way it sits right now would look a bit better with larger diameter tires on 15" wheels to help fill the wheel wells better. But, if it's lowered a bit more?.. the wheels and tires being smaller in diameter may not be so obvious without the larger gaps around them.
I have the same exact tire/wheel combo on my grabber. It looks way better now after I cute 1 3/4 of a coil off. It still turns full chock too!
I really hate the rims it sits on right now, i plan on replacing them as soon as possible. I put larger tires on the front last year because when i bought it they were really small.
The car is really sharp!! I would lower it and go to 17's if it were mine. My 74 Grabber is currently stock and appears to be on stilts when sitting next to my 2006 Mustang GT.