Orpheon is pretty far along, it will probably take the longest, due to the fact that I have to make the entire thing out of 'solids' through the editor. (Solids are rectangular prisms, no other shapes. >_<)
Tallon Overworld was pretty close to done, but we have started over on it, for various reasons. The new map is MUCH better, and about as far along as Orpheon
Phendrana Drifts is the closest to completion, by far, as we have the entire map roughed out and ready for detailing, which is decently far along as well.
Magmoor caverns is just getting started.
So I mean, we have a good bit done, but yeah, we're in it for the long haul. I'm planning on using it for my application to various game studios.