I haven't received the drive yet, so I am not set up as you are for 2015 ..
I'd suggest installing RB to your C: drive and running it from there (at least as a test).
Leave the realtracks/realdrums on the external drive during setup if space is an issue.

To start troubleshooting;
Does RBSeq32.dll exist in the directory you think you are are running it from?
It should be in the Realband folder.


I do not work here, but the benefits are still awesome
Make your sound your own!