I am using SharePoint Online which is running SharePoint 2013. When I visit the Site Settings page, it looks like this:
Whereas on SharePoint 2010 it was:
What is the reason for this? Is it something to do with 2013 on-premise running 2010 deployed solutions and having them in the 14 hive folder? Maybe I'm way off the mark but I'm wondering if it has 15 in the URL as it has to support 14 as well.