Something I had noticed is that Office 16 is shown in Start Menu in a Office 2013 folder (version 15) and all apps are renamed as such. Don't worry, actually is version 16 and you will notice it after running for the very first time.
6 May 2015 update
If you don't have an Office 365 subscription, you can download a trial version of Office 2016 Preview here:
Product key for the Office 2016 Preview
The Office 2016 preview will expire only when the final version of the software is released. You can send feedback to Microsoft by clicking the smiley face icon in the top right corner of any Office app. You cannot use the Office 2016 Preview side by side with Office 2013.