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I'd be curious to see what images cause your layout to load slow though. I've pretty much never managed to get layouts to take much longer to load than the blink of an eye, to the point where it was so jarring that I added a fake loading screen (fade to black)
This is easily accomplished on inexpensive Chinese phones, their built-in memory is very cheap and slow.
It is not critical, but at the first loading of large sprites there is a certain lag and the eye can notice it.
Therefore, I load all the leaf environment at once and create opponents outside the visibility only when the hero begins to approach them.