It may not be helpful, but still useful to know that for most CC 2015 users, there is no speed lag. So it’s something on your system.
I assume you’ve tried rebuilding your prefs.
Try this:
1. In Prefs > General, disable “Show “Start” workspace” and “Show Recent Files Workspace”
2. In Prefs > Type, set the Number of Recent Fonts to Display to 0
3. In Prefs > File Handling, set Number of Recent Files to Display to 0, and disable Check Links Before Opening Document
Restart InDesign and see if that helped. They all have to do with InDesign searching for things that it’s having trouble finding. All suggestions came from users on various threads where they said they had the same issue and one or more of these fixes worked.
One more possible operation that helped some folks with general slowdowns:
https://helpx.adobe.com/creative-cloud/kb/creative-cloud-libraries-panel-doesn-t-load-in-desktop-products.html
Let us know if any of this helped!
AM