The calculated distance (air line) between Montfermeil and Paris 15 Vaugirard is approximately 13 miles respectively 21 kilometers.
By car or train, the actual journey to Paris 15 Vaugirard is certainly longer, as only the direct route (as the crow flies) between Montfermeil and Paris 15 Vaugirard has been calculated here.
Air line (approximately)
21 kilometers
12 nautical miles