What were the fewest amount of guns possessed by a frigate that served in 1815?
CREATE TABLE "ships_served_in_by_adam_bolitho" (
  "ship" text,
  "guns" real,
  "class" text,
  "captain" text,
  "rank" text,
  "year" text
);
SELECT MIN("guns") FROM "ships_served_in_by_adam_bolitho" WHERE "class"='frigate' AND "year"='1815';