I have the opportunity to get some 15'' wheels with new tyres. Ignoring the aesthetics what else will I notice going from 205/55/16 to 195/65/15? More comfortable ride? quieter?

You'll see the bumps going under the car but you won't feel them at all. That's the way the 15" wheeled Octy's I test drove were anyway. On the 16's on the current car bumps are noticeable, but still not harsh. I wonder will the rear feel less fidgety through bends with 15" wheels too (At the expense of feeling for grip)...

You'll see the bumps going under the car but you won't feel them at all. That's the way the 15" wheeled Octy's I test drove were anyway. On the 16's on the current car bumps are noticeable, but still not harsh. I wonder will the rear feel less fidgety through bends with 15" wheels too (At the expense of feeling for grip)...

I test drove a basic Octavia with 15" rims. I bought mine with the 17", the difference is very slight and it still has a decent ride to be honest. I did test drive mine before handing over the money. The smaller tyres will be cheaper to replace and they may be slightly better on bumps.