Hi,
As far as I can tell, if we want to activate Office 2016 Preview, we need to have an active Office 365 Business subscription. Please check
this thread, it seems that this only applies to some certain plans, such as Office 365 ProPlus, E3, and E4.
Anyway I can't guarantee the currency of the information above, as Office 2016 Preview is a self-supported program, we are not offering technical support for Office 2016 Preview right now.
You can try for help from the
Community where you can ask questions and get answers from other preview users.
Regards,
Melon Chen
TechNet Community Su