http://simplemachines.org/download/
At the Large Update and Small Update for SMF 1.1.5, those two say "1.1.3". Not sure if this is a typo or not?
It is a bug it should actualy say 1.1.4.
Why? Because if your not upgrading from 1.1.4 you need the small update. But anything less, and you'll need the full update.
I'll add it to the tracker.
Bug #2009: Wrong version No. of Downloads page (upgrade for 1.1.3 instead of 1.1.4) (http://dev.simplemachines.org/mantis/view.php?id=2009)
Great I this after issue after updating (Small Update) from 1.1.4 to 1.1.5. So I manually copied the Large Upgrade to overwrite the files which now displays 1.1.5.
EDIT
Yes I did delete the upgrade.php file :)