I'm not sure if I understand all new comments correctly and inhowfar they would refer to the original problem described, but I can tell that I also have the bookmarks' icons (or the particular bookmarks icons feature in Opera) under suspicion for causing the high RAM use and also the long time it takes for relaunching Opera.
Background is that this feature is important for me, because I like to indentify bookmarks and especially different bookmark types with icons. In that, this is a crucial feature for me.
There are at least two indications for this as a major root of the problem.
1: When setting a new bookmark I mostly have to change the icon of the bookmark in a 'second step', i.e. basically an additional setting of the very same bookmark. This slows down Opera twice in short time, which burdens RAM use as well as the operarion of the CPU (you can hear it clearly). Furthermore, such bookmarks setting of more than one bookmark increase RAM use little by little as described above.
2: Relaunching Opera after a breakdown or regularly seems time-consuming because of this particular feature (i.e., loading all bookmarks WITH correct icons assigned). This is obvious as it is one of the processes during the relaunch that seems to last forever).
So, considering the very high number of bookmarks creating a large bookmarks file, this might explain the high resources consumption by Opera. If there are indeed such things is background update of icons of bookmarks, i.e. even for tabs not opened, this seems to be even more plausible. Similarly, if Opera works in a way to have ALL booksmarks with correct icon 'ready' when Opera is open I should probably not wonder at all ...
I have one addtional small problem since today for which I'm not sure if it is relevant for a new discussion:
Opera has changed some settings, but not the entire language, from the language I use in Opera to English. This would not worry me that much. However, I'm wondering if it could indicate a more relevant bug. But perhaps it disappears with the very next update.