150 grit is REALLY heavy, I'd never tried this even when the ball was messed up, because it will leave very deep scratches. Best advise is to have it resurfaced in a pro shop. I have seen woundrous things on a Ebonite Predator which was BADLY marred (5mm deep and wide!) and looked as if used in WWII against tanks. When it came back, only the deepest cracks were visible, amazing.
If you are to sand a ball surface to get deep scratches out, I would recommend not to bet below 400 grit - and even this is a lot. It is better to be patient and sand the ball a while, rather than doing it with violence and pressure. Heavy abrasives can, besides scratches, be dangerous for the track area, which could lose its circular shape! Sanding on one spot may even influence the ball's mass distribution?
I highly recommend 3M pads, used under flowing water. They are very strong and give a very good result at home. I haven't used compounds by myself yet, but for surface finishing they should do a good job?
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DizzyFugu --- Reporting from Germany
"All that we see or seem, is but a dream within a dream..." - Edgar Allen Poe