I'm not sure about what speed you would get, but I'd assume that your program would run
nearly as fast as it would if you hid all those spheres. Not quite as fast as it would go if they didn't exist but, since it's not needing to render any polygons/textures/lighting/whatever, but still needs memory and processor bandwidth because the object is still there.
Also, the command you're thinking of is: "hide object xx" Where xx is the number of the object you want to hide.
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