Hi Garry,
Welcome to The Hub!
EXOS 16.x was recently released. v16.1.1.4 is the only version available. Is there a particular feature you're interested in that is driving you to 16.1?
If you haven't seen it yet, take a look at this post:
EXOS 16.1 Releases with New Hardware and Role-based Policy Support!
I would also recommend you review the Release Notes (on the support site) and the "proactively published" articles mentioned in that thread.
As Patrick mentioned above, you shouldn't have any trouble moving from 15.3 to 16.1. Remember that the X430 uses the "summitlite" image, whereas the X440 uses the normal summitX image.
Let us know if you have any other questions!
-Drew