Lapping Question when you have limited options

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I was planning to lap my HSF before using it and read well on the methods but the hardware store here got only the 600 Grit and the 1500 Grit. An automotive store here have the 600,800,1000,1500,2000 Grit but they sell it in packs (like $5-$7 a pack) and I don't want to shell out that much for that many sandpaper. Can I use 600 then jump to 1500 grit? Or can I use 1500 Grit until the bottom of the heatsink smoothens out?