There are things to consider. The GMs need to make sure of the legitimacy of your guild. Im sure they've had people in the past try to get extra DS necks and such. Im not saying you are, don't mistake me, I am just explaining the things they need to check. For example, there's a difference between having 15-20 people in faction and 15-20 active people. As well as there being a difference between 15-20 online per day and 15-20 online at a time. As well as the number of people in your guild in total, how long it's been established, how many chars may be alts.
In all honesty, I haven't really seen your guild around very much, so you may not meet the activity requirements just yet.
Just be patient and keep building your guild. Perhaps try contacting a GM or Aga personally to find out why your guild may not have been accepted as of yet.