A Col# is the collection. It corresponds to a software or course version. Thus, TFIN50_1_EN_Col10 and TFIN50_1_EN_Col15 are respectively collection 10 and collection 15. The higher number should be a more recent software version or course.
SAP should spell out the meaning of these suffixes more clearly. I, too, did not know what they meant when I was initially looking through the available courses.