@cafeochomx
My about 40 tabs consume 800MB either. Is that actually a problem? I've got some gigabytes free, Opera could consume up to 6GB or so, I would not notice.
But as this 800 MB is for single tab and seems a bit too much, press Shift+Esc and note down, which Opera sub-processe consumes most memory. It is likely some extension, be it Opera internal or some external one.
Opera for Windows