What was the highest number of extra points scored by Albert Herrnstein, when he scored more than 15 points total?
CREATE TABLE "michigan_63_oberlin_0" (
  "player" text,
  "touchdowns" real,
  "extra_points" real,
  "field_goals" real,
  "points" real
);
SELECT MAX("extra_points") FROM "michigan_63_oberlin_0" WHERE "player"='albert herrnstein' AND "points">15;