You have a free phone and the XZ currently works way better on Marshmallow. All apps will be supported for the life of the phone so why worry about installing what amounts to a beta version of Nougat?
As @uliwooly already mentioned, prototype devices are not meant to be sold. I would appreciate if you could send me a PM with the following information.
IMEI:
Where was it purchased from:
Date of purchase:
IMEI can be found in Settings > About phone > Status > IMEI information, or by dialing *#06#.
