Hi Mouran,
I am sorry but this doesn't work for me. I am on Outlook Mac 15.6 (so as you) and I tried to add the conference's room in the "People I am Delegate For" (with success) and still after half-an-hour and several close/restart of Outlook, I still can't accept the reservation request because no ACCEPT button shows up yet. I am wondering if this is can have something to do because I have TWO supervisor that can accept or refuse the room's reservation... but I don't think so because it work A1 in OWA (Outlook Web Access) and also A1 on Outlook 2013 on Windows... God damn Apple computer! :-(
Here's a screenshot (sorry I am in french canada, but you'll still saw the issue...
Thank you very much for your support!