My company has been using version 12.6 and now I see version 15. Did we miss a release?

You did not miss a release. In October 2003, Rasmussen Software released a major revision of AnzioWin and Anzio Lite. However, due to our international community of users, versions 13 and 14 were not released. Version 15 is what we started shipping after version 12.7.