A new version of ts2015 is out which does some minor updates to steam API... nothing fixed yet, and nothing new.
To go back to the previous version (48.9a) so that TIR4RW6 works :-
go to plugins directory of TS2015
rename gamemanagerVC.dll to gamemanagerVCxxxxx.dll (if your on AMD cpu, otherwise ignore)
rename gamemanager.dll to gamemanager49.4A.dll (so you can rename it back if needed)
COPY over the previous version of gamemanager.dll (48.9a) from your backups.
You do have backups right? Always a good idea to make a backup of TS2015. I just create a zip files of all files, excluding the assets and contents directories which are huge. Also exclude manuals and language folders to save more space. About 100-200mb when compressed.
That's it. Hopefully no bugs introduced. Both leds should turn on on your trackir when TS is started to confirm it's working.