Running out of VRAM on iOS

No, you will also need to access the Sprite and Texture Atlas assets and unload them via https://developer.playcanvas.com/en/api/pc.Asset.html#event:unload

A small example can be found here for scene loading but same process: https://developer.playcanvas.com/en/user-manual/packs/loading-scenes/#managing-assets-in-scenes

Draw calls shouldn’t matter.

I don’t understand why loading really quick would crash it? Maybe you have a different issue that is dependent on timings/race conditions? Do you have an errors or logs in the devtools console when that happens?