I've been doing the same thing! When I do other watch faces with lots of black background, it rather seems like an S6. So I find I keep doing photos or light-colored backgrounds, so each time I look at it, I go whooooa.They're 155mm - I just measured it. I thought they were 165mm LOL
I always get an extra hole added at the Hermes store.
I LOVE it. I think it's the full screen watch face that makes it feel bigger. I'm using the Hermes Circulae face now and it feels no bigger than the S6.
That's a big difference 165 to 155 -- as far as band sizes, so it's good that you just measured!