Firstly just to confirm it is a DS115, not a DS115j?
Please be aware, I am just going on the info I found, so take this advice with caution… and feel free to wait for more a knowledgeable answer.
If it is a DS115 then maybe try one of the downloads from the last post on this thread
(as the main downloads page may not be providing the latest versions):
As according to this page:
Yours is listed as an x15 series, so I would have thought looking at the downloads links, you would want this one:
