From A + C = 6, we find that A and C weigh 6 kg together. Since P + Q + S + D = 15 and P + Q + R + B = 17, substituting Q = S and P = R gives us 2P + B + D = 17. Since D from the first equation (A + B + C + D = 17) can be substituted in, the weight of P and Q can be shown to exceed 6 kg, confirming that P and Q weigh more than A and C combined.