Hi Phil,
If I recall correctly the KS-15 and KD-15 Johnsons were some of the earlier 9.8hp alternate-firing twin cylinder outboards from 1941 and 1942, but neither was considered a race engine. The KS (S=standard) had a rope plate so it could be rope started and the KD (D=deluxe) had a rewind starter. In the early 1930’s, Johnson built a KR-55 racer. The letter "R" signified racing. This was also true of some of the other race motors of that era.
I will also point out that just because the original KS-15 was not a racer, that does not mean that some racing fanatic could not have modified it making it a racer. If you can post a photo of your motor, our members may be able to answer that question for you. I hope this information is helpful.
Tom