M_Boats: Rudder length

Having just bought a M-15 from 1980, I am wondering if the rudder that I have is the right length and weight. This one is made of teak, solid teak over an inch thick. What is the length of the standard rudder for a M-15 and it will be used for cruising and day sailing, not racing if that makes a difference. I sure appreciate the combined knowledge and experience of this group. I saw it in action today in regards to another issue that came up here. Thanks. Doug M-15, 1980