When you have very large parts it's time consuming to consider the whole cavity.
It could be helpfull to mesh just 1/2 or 1/4 of the part and apply an option of simmetry boundary condition for cavity mesh (both dual domain and 3d).
Usually the hot runner producers are splitting the cavity to save time but the real flow front at the simmetry face could be slightly different.
If you have this option at least for fill you can save time in balancing the flow and then consider the whole cavity for pack and warp as usual.
