So I guess it's an issue you should ask about in the game thread instead, you may get better answers there.
One thing that could happen with Ren'Py is a build-up of image layers in the memory in case the dev is using a lot of
show
statements without a
hide
statement for each of them or an occasional
scene
statement that would clear up all the layers.
That would be a specific game issue.
Another is a possible memory leak. That would be a Ren'Py issue, specific to the version used by the game.
You could try to limit image cache size by setting
define config.image_cache_size = 8
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. Worked for me in another game.
or
define config.image_cache_size_mb = 300
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. By default the value is
None
and config.image_cache_size is used.