Mr neat and tidy (your profile shows that as your name). I know the size is 205/55 in 16".
You take a 16" oem rim with 205/55 and a 15" oem rim with 205/65.
The 15" would still be lighter.
And even. If you take 15" rim of a civic with oem size euro crap, and the same another rim with 205/65 cc5. The rim with cc5 will be lighter in weight. So yeah. Other senior members would agree to this, if not you atleast.
And we are not talking about dia here. We are doing a 195/65/15 vs 205/65/15. And in this case for a 9gen civic.
And please note. Its not just the dia or the width that matters. Weight of tire plays an important role too.