15.5 mile swim?

Today I ran 15.5 miles rather slowly (2.5 liters of water). I must have hit the wrong button on my running app because it logged this as a swim. It was overcast and 85 degrees with 60% humidity. I've been trying to do these runs without taking in any calories. I don't think I am going to keep this up. I think I run better when taking in a few hundred calories. It doesn't matter to me if the effect from the calories is real or in my head.