How to remove JPAGE_CURRENT_OF_TOTAL after 1.5.15 upgrade

The problem is the lack of appropriate language pack for the installed version of Joomla. JPAGE_CURRENT_OF_TOTAL is in fact a "code representation" of the sentense "Page x of z." and the reason you seeing it this ways is because your current language pack doesn't have this sentence in it. This string actualy belong to the Joomla pagination plugin.
Solve it in 2 ways:

1. Download a matching language pack for the version of Joomla you're working with.
2. If the language pack is just not available yet, fix it manually:
   
   
   • Locate the main localization file - so if you have Finish installation it would be: <Joomla folder>\language\fi-FI\fi-FI.ini
   • Manually add the following line in to it:
     JPAGE_CURRENT_OF_TOTAL=Page %s of %s
     You probably will want to translate it to your own language before.