For what it is worth, I am running a set of Kumho Solus KH16s on my 2013 ST-S right now in the 155/60-R15 size. I just didn't know if I could fit 175s in there. The 155s are 10mm narrower than the OEM tires, but you do not notice it while riding and barely notice it looking at it, you really have to be looking for it. If anything you visually see the different tread. They are rated treadwear 440, traction A, temperature A, load rating 74 T.
So far I am very happy with the immediate difference in how the machine felt and drove, almost like when I bolted in Ron's sway bar and the Fox shocks, nice improvement in feedback with less body roll and they track nicely. They are wearing even so far, at this time I have no complaints or reservations, I will buy them again, but would love to try the 175/55-R15s next time if I knew they would fit. At like $70 each they are a good value, but I would like more of a summer performance tire, but the options in either of these sizes is also quite limited.
As a final note, I do not baby my Spyders, I push them quite hard, typically 200-300-400-500 miles per ride at high speeds, I am not taking it easy on the tires, they are getting worked. In case that helps. I am not gentle on them. My rear tires usually only last 4,000-5,000 miles, and that is using car tires also, Toyo Proxes 4 right now, they are rated treadwear 300, traction AA, temperature A. Seems they are now out of production as well, I bought up the last 6 of them I could find a while back, only have two left. nojoke