6 is way too little, at the very least it should be 9, but that's the bare minimum, it should be even higher. It's not intensive, there is no reason for it to be capped at 6. Collages aren't always for memories and stuff. Collages can be used to showcase, for example: your favorite anime characters, that should be a 3×3 at least, 6 isn't enough.
And I say this because I genuinely love the gallery app, it eliminates the need for editing apps. Please raise the limit Samsung.