If it's at 1500, then every step you make with the abrasives (2000, 4000, etc.) will add length, PLUS the length you will achieve by adding polish. Unless you bowl on the Sahara Desert you may get the proverbial over/under reaction.
I prefer to use some grit under my polishes and/or compounds for my taste. It's very common for me to go 500, then skip directly to the "shine" phase. I can always add an extra coat of polish if needed later.