CREATE TABLE table_21314 ("Position" FLOAT, "best year" TEXT, "best 2-year period" TEXT, "best 3-year period" TEXT, "best 5-year period" TEXT, "best 10-year period" TEXT, "best 15-year period" TEXT)

Which people had the best 10-year period when Capablanca had the best 15-year period?
SELECT "best 10-year period" FROM table_21314 WHERE "best 15-year period" = 'Capablanca'
SELECT "best 10-year period" FROM "table_21314" WHERE "best 15-year period" = 'Capablanca'