It looks as if you are trying to use the dimensions I gave you. If so, there are a few minor things you would have to change. As Ryan mentioned, he has had better experience with the subwoofer on the same plane as the port. In my suggestions before I had mentioned a height of 16". With this height, that leaves you with enough room of the 14" cutout and 15" sub on the face, where I have it relocated.
As for the port depth issue. As the port runs back into the box, the port area must ALWAYS remain the same. In order to do so, you must keep the port width equal at all times. In your case, you want to leave a 3" width/gap. Therefore, your port will need to bend. (see diagram.)
I did my best in a quick paint fix-up trying to show a few things graphically. lol
