Hmm.. yes , I've just had a look and it appears my research maybe incorrect.
The sprocket number is correct but it may not be available in a 15 tooth.
You'd have to reduce the Size of the rear sprocket .
The number is JT 823, standard is 47 tooth and they make 39, 41, 45, 46, 47 & 49 .
45 would be a good shout but you'd have to check you've got enough spare adjustment to take up the slack .