I have a wire chart instruction sheet in my hands from a different manufacturer. It is most likely the same chart. Most likely the same pump as it has the same info. Mine says that the #10 for 15' would be for 3% voltage drop. You can use 10% voltage drop and be within specs. Mine has 2 columns. #14 is good for 15' @ 10%. Keep in mind, that is total footage pump to battery and back to pump. So you are talking 30' of wire. Mine will be 50' total and I will be using #12 per my chart at 10% voltage drop. It does work out. I am a master electrician. I have not done the hard math but I do know that #10 is way overkill for a 15' run. This makes for a much easier installation. The pump will dump a 40 gal tank in less in 4 min. I'll be using a 12 ga extension cord and blue crimp connections.I will be pumping 50' thru a standard 3/4 garden hose per the instructions.