The description of Endurance of the Berserkers says you are still acquiring Fatigue levels, and contains "If you run out of Fatigue levels, the spell terminates immediately and you fall unconscious.". So I expect a Sun duration version would have the same limitation.
It is from Base 10, presumably the guideline "Eliminate the penalties of Fatigue and wounds."
I agree that base 15 guideline seems to be made for flying rather than levitating.
I was thinking along the lines of Gift of the Frog's Legs ReCo15, where the target makes a token jump, which is unaffected by any actual running start that the character may or may not have.
My hypothetical "Atalanta's enduring footrace" ReCo30 would be similar. The target isn't actually running, just making token leg movements and the body is magically propelled in the appropriate direction as if they were sprinting.