I'm looking to purchase a (used) Bianchi SISS (I'm opened to offers if you've one available). I'm well aware of the chainstay issues but would like to concentrate on deciding between a 15.5 and the 17.5 (I haven't been able to peronally test ride either size). I've seen similar threads regarding sizing on the SISS, but not for a smaller rider such as myself.

I'm 5''8" with a pants inseam of 30" and a cycling inseam of 32". Anyone sized similarly and with experience on the bianchi?

Any help will be greatly appreciated. Thanks!