Hi Monica,
If you open the .Wor (from the workspace location) in Notepad, you will see something similar to the following at the top....
!Workspace
!Version 1600
!Charset WindowsLatin1
--------------------------------------------------------
Change the Version stamp from 1600 to 1150 and click File > Save in notpad. Then try opening the .Wor in MapInfo Pro 11.5
Please note: (backwards compatibility issues with new features)
If you have used any of the new features such as legend designer in the workspace using MapInfo 16, It may not open up successfully in MapInfo 11.5.
See this article for more information: https://li360.pitneybowes.com/s/article/How-to-create-a-MapInfo-Pro-Workspace-and-use-it-in-older-versions-of-MapInfo-Pro
Let me know if this helps you. Thanks for posting!