On the Mac, Xcode's "Playgrounds" are super useful for quick experiments but, due to their nature, terribly slow for "real" tasks.
If your code is more than a few pages long, and/or involves working with the UI, as you do with SpriteKit, the Playground may become really slow, sometimes even unresponsive.
"Playgrounds" are part of Xcode and run on top of the iOS simulator - that's how they display graphics and UI in the "Assitant Editor". The iOS simulator is not really known to be fast either.
On the other hand, "Swift Playgrounds" on iOS is a completely different app, even if it shares a lot with its Mac cousin.
Most importantly, it runs in iOS on the real device, with the real hardware processing, not emulation, which makes it ideal to use for SpriteKit, as Apple themselves often shows in their demos.
I would therefore say that your code should indeed run faster/better/properly on the iPad version.
Even if of course, I can't really know, since I don't know your code - you will probably be the one telling us later if using the iPad version made a difference.
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