all you have to do is create your models at startup but create them as view entities, that way, when you load your level, there will be no delay when creating them ...

[MANUAL]
"After an entity is removed, its file content is still stored in a cache for faster creation of entitities of this type. The cache is emptied when the level is changed. If this is not desired for some reason, keep the file in the cache by defining an invisible view entity with the same file. "