The "Teamleiter" would be the "Functional Supervisor" or in this specific case the "Team Leader". In English, the term "Disciplinary Supervisor" is usually only used in education organizational contexts. In business contexts, the "Disciplinary Supervisor" is more often referred to as the "Administrative Supervisor".

In your example, the writer probably wants to emphasize that s/he is wearing both caps. S/he is probably the functional AND administrative manager of the group of 15.

HTH

Dan