Yes, it will do purely because there’s less black area on the screen when using the Siri face. Whether this would noticeably use more battery would be debatable.
Stupid question I know but my watch is going to low power 10% thing at about 6pm. It use to last all day. Is it because I have changed the face to toy story lol. I thought it was the last update that caused. But I changed it to the toy story at the same time. I have only just put two and two together when I seen this thread