I've just open v2015 to see how it reacts with AS. I've simply created a new document with an empty text box and decided to see first wether regular Quark AS scripts shipping with the software would or not run properly. So I chose Box Tools > Make Caption Box.
I was surprised to see it works perfectly
So I open the script in my AS editor. I've run the script from there (gosh! © 1986-2006!) and bad luck: it errors "Impossible de convertir "60,286 mm" en type point units. [-1700]"
Don't know what to think of this. It means that our scripts would run properly straight from within Quark but we'll get white hair at blind-coding and testing our stuff.
I don't know nothing about Osaxen but I have the same feeling that the OSAX might be somehow obsolete. Don't know.