It's is 100% free, and I assume the area's are enormous.
Atleast many many times than the planet maps.
It's gonna have to, if they are gonna be able to have the option to fit the Executor in the game should they decide to do so.
If the space was the same the ship would never fit.
Unless they go with the 12.8 km lenght.
Still, a 15x15x15 km playground would still be waaaayy to short even for that size.