I did the same on my similar leg as to your 14-15, looked at it for a while before seeing the gap. The map started to rub off a bit too - there was one thick black line later on that had been on a fold and looked like it was passable. Fun race though, shame about that street being closed.
Yeah that gap near the Business school (16-17) is a bit small... but if that's the only one I missed, it's not bad going.
I missed the gap on 14-15... Thought it was an outbuilding... So went back past 13 (almost)... Cost me 4mins :((