What is the 20-year peak with emanuel lasker, 2816 as the 15-year peak?
CREATE TABLE "chessmetrics" (
  "rank" real,
  "1_year_peak" text,
  "5_year_peak" text,
  "10_year_peak" text,
  "15_year_peak" text,
  "20_year_peak" text
);
SELECT "20_year_peak" FROM "chessmetrics" WHERE "15_year_peak"='emanuel lasker, 2816';