When testing on my 15.10, I find that if I hold down the <Super> key, the Keyboards Shortcut window is shown and the first 10 application icons in the Launcher are numbered. And yes, if I press a number key while holding down <Super>, the application with that number is started (or, if it was already started, becomes focused). Involving the <D> key makes no difference for me.
Thanks for your report!
When testing on my 15.10, I find that if I hold down the <Super> key, the Keyboards Shortcut window is shown and the first 10 application icons in the Launcher are numbered. And yes, if I press a number key while holding down <Super>, the application with that number is started (or, if it was already started, becomes focused). Involving the <D> key makes no difference for me.
Can you confirm that behavior?