10-15’ should not be an issue. DC current IS sensitive to distance, but you can counteract that by increasing the gauge of the wires. Make sure you use appropriate sized wires that will handle the amperage over those distances. Its also no difference if the two batteries are next to each other and then there is a long run to the motor, or if one battery is close to the motor and the other is long way away. Sent from my iPhone using Lake Ontario United