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Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download Scene Pre-Loader Free.
Scene Pre-Loader v2.0
Scene Pre-Loader for Unity allows you to send all your GameObjects to the GPU when the scene starts, forcing the GOs to be loaded and cached in the GPU. The Scene Pre-Loader includes a progressbar with optional game hints, which show the progress as the items are cached.
Pre-Loading your GameObjects can also speed up your level as the player progresses, as it reduces lag/slowdowns when new GameObjects are instantiated into the scene.
NOTE: Requires NGUI
Documentation
Demo
Forum
Includes a free version of NGUI