Welcome Boodlums!
All of the forum's pages say how long it took the system to create them. Most take only a second or two - some are even well under a second. However, on some of the pages, particularly the ones like the posting page, the icons can take a bit of time to initially download. SMF tries to make the filesize of thier icons as small as possible. But, of course, sometimes you just have to balance size against functionality.
At some point in the future, members will be able to decide in their profiles whether or not they want the BBC icons to display on the posting page or not...