Can you have 15 Copies of Microsoft Office on a single subscription?

Yes, when you purchase one subscription of Microsoft Office 365, you receive the right to install 5,5,5 copies of Office on different devices for that single user. We have highlighted the following points that speak to this licensing fact:

From Microsoft Official Volume Licensing Documentation*:

Italics are ours for clarification or emphasis:

1. Each user to whom you assign a User SL (Subscription License) may activate the software for local or remote use on up to five concurrent OSEs (Operating System Environments). (5 copies for Windows and / or Mac)
2. Each user to whom you assign a User SL may also activate Microsoft Office Mobile software to create, edit, or save documents on up to five of their smartphones and five of their tablets

In our words:

Each user of Office subscription, E3, or E4 can run up to 15 copies of Office - up to 5 that are full function 2013 (PC or Mac) AND up to five on mobile phone AND up to five more copies on tablets (currently only iPad Office is available – Android tablet to follow at a time that is unclear). Additionally, any user who has access to the web applications (K1, E1, E3, E4 plans or a-la-carte) could access Office functionality via any modern web browser.

Need a quick comparison chart? https://www.interlink.com/component/easyblog/?view=entry&id=26

*To check out the details, please see the Microsoft Office Services Use Rights Document and lookup Office 365 ProPlus:

http://www.microsoftvolumelicensing.com/DocumentSearch.aspx?Mode=3&DocumentTypeId=31