15.5 km is harder than 21.2 km. Huh?

It's true.

This past Sunday, I ran for two hours and covered 15.5 km.

Afterwards, I was thinking how tough it was. Tougher than running a half.

Much of this I think is the lack of a crowd and friends. Even if my friends are nowhere around (because they're all way faster than I am, natch), I have more spirit, more adrenaline, somehow it just seems easier.

What's your experience been?