The overwhelming majority of the world's Orthodox Christians use the Old Calendar exclusively.
The Churches of Russia, the Ukraine, Byelorussia, Georgia, Serbia (I may be missing some various Slavic churches) all use the Old Calendar. Also, the Jerusalem Patriarchate, the monasteries of Mt. Athos and various other Greek-speaking monasteries around the Mediterranean use the Old Calendar.
None of these Churches or monastic institutions show any signs of being interested in changing. One of the reasons is that if you follow the full Orthodox cycle of services and feast/fast seasons, there are a number of things just don't work right on the "New Calendar", and this is one of the reasons why many monastic institutions prefer to retain that calendar. But that is another story...
(I attend a parish that follow the New Calendar, BTW...)
So they wouldn't be commemorating St. Andrew today then?