Girl sperm V Boy sperm

Can any1 tell me when to stop bding to try and sway our chances of having a girl!?! My fertile window is 12th-18th, and hubby and I r thinking if we stop bding on the 15th then the girl sperm will b waiting...we bd on this morning, and planning on bding on the 12th, 14th and possible the 15th.....is the 15th too close to Boy sperm territory?? Any advice would b great xx