Complex sentence: A further batch was ordered in 1931, though this coincided with a downturn in the volume of freight due to the economic depression, therefore dictating that the last S15 4-6-0s were not completed until 1936.
Split into simpler sentences: A further batch was ordered in 1931, though this coincided with a downturn in the volume of freight due to the economic depression. This meant that the last of the third batch of S15 class 4-6-0s were not completed until 1936.