Silicone spray is too lightweight and it is likely going to dry out on the slide from the heat of the sun before you can even make one cycle. You should get you some cooking lard or other heavy industrial lubricant that thick and lather the slide down in it.
This will make you go faster, especially when it rains. However it is very likely that it will also total the slide if it dries or is not removed.
*For information purposes only.