Preloading files will not magically remove all the ent_create time. The engine loads files very fast and buffers them in a cache anyway, so you won't gain this much time with a preload process.

Creating entities is a very different process than file loading. Much time is required for DirectX processes, such as building a mesh on the 3D card, building textures, creating the lighting, and creating a collision mesh. This can be sped up a lot by a clever concept that creates entities in several steps.

When you create entities first with INVISIBLE,NOLIGHT,and PASSABLE flags and have collision_mode at 0 at creation time, you'll see that creation is much faster. When you need the entity later, just reset the flags.

You can see such a concept in the infinite terrain demo that creates ten thousands of entities in a second.