For loop execution times in PostgreSQL 12 vs 15

I am running a simple test and am curious to know why a difference in execution times between PostgreSQL 12 vs PostgreSQL 15.

CREATE function test() returns int language plpgsql as $$
declare
      v_number bigint;
      v_multiplier float = 3.14159;
      loop_cnt bigint;
begin

      for loop_cnt in 1..1000000000
      loop
            v_number := 1000;
            v_number := v_number * v_multiplier;
      end loop;

      return 0;

end;$$;