running 6A dc motor with 15A
15A is max. current which can be safely supplied by the driver. However motor rated at 6-7A continuous will draw somewhat more current at the beginning for a short while. Typically this is not a problem with most of motor drivers driving 7A rated motor, but you might want to check data sheet of your driver for the same. 

Also in case motor stalls (i.e. motor cannot meet load torque requirements, may happen when motor has more mechanical load than it is designed for.), windings may get damaged if not properly protected.