user: Question: What is the highest rank when Anatoly Karpov, 2820 is the 15-year peak?
Columns: ['Rank', '1-year peak', '5-year peak', '10-year peak', '15-year peak', '20-year peak']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Bobby Fischer , 2881', 'Garry Kasparov, 2875', 'Garry Kasparov, 2863', 'Garry Kasparov, 2862', 'Garry Kasparov, 2856']
SQL:

assistant: SELECT MAX("Rank") FROM "Table" WHERE "15-year peak" = 'Anatoly Karpov, 2820';