In 2015, Microsoft released Office 2016, but prior to that, there wasn't an official "Microsoft Office 2015" version. However, Microsoft did release Office 2013 in 2013, and it was widely used. Some users might have referred to Office 2013 as "Microsoft Office 2015" due to its popularity and longevity.
For an older version (like Office 2016 64-bit trial), search for "Office 2016 Deployment Tool for IT Pros" on Microsoft’s website. Microsoft Office 2015 Free Download 64 Bit
You may be seeing "Office 15" in your file folders. This is the . Office 2010 = Version 14 Office 2013 = Version 15 Office 2016 = Version 16 ⚠️ A Note on "Free" Downloads In 2015, Microsoft released Office 2016, but prior