Green’s Dictionary of Slang

fifteen and two n.

also fifteen-two

[rhy. sl.]

(US) a Jew.

1935		A.J. Pollock Und. Speaks.
1946		St. Vincent Troubridge ‘Some Notes on Rhyming Argot’ in AS XXI:1 Feb. 46: fifteen and two. A Jew. (Origin uncertain, but probably American.) Almost certainly American.