Roger,
15 carrier planes are notorious for feeling very light on the lines during low speed. I have an adjustable line guide on my planes (it's not a slider, I can adjust them on the ground and then they are set for the flight). I set them with a as much rake as I can and still have decent control at high speed (I'm guessing they are about 15 degrees to the rear). It costs a bit in overall speed but during low speed it helps a lot. Remember to launch the plane at an angle so the lines are straight, this means that the plane points outward at launch. You can also use more motor offset too. I use about 5 degrees motor offset.
Don't know where you can get yellow props.
I use 7X4 APC props on my Cox Conquest, they seem to work the best. Try different sizes depending on the motor.
The rules state .012 stranded or .010 solid liines, 52' to 52'6" in length.