The D7200 is supported in Lightroom 6. What happens when you try to import? Any error messages? What operating system? How were the images transferred to the computer? Did you use an older version of Nikon Transfer?
When I try to import into LR 6 I get message "not all files can be read and are not imported" and then the number of files I try to import.
My Import comes directly from de memory-card I put in my Macbook Pro. (latest software OS El Capitan).
If I try to import with Nikon Transfer there are no problems,
Strangely I CAN then import them from the location " my pictures" into Lightroom.
But not straight from the card.
A "file could not be read" message usually indicates that there is a read/write permissions issue with the destination folder.
Thanks, I deselected to copy to my NAS and voilá it imports the NEF's.
Now I know where to search to solve that latest (copy to NAS).