Originally a circuit involved an aerodrome and an aeroplane. A properly flown circuit would be different for each aeroplane if you wish to maintain the runway on the wingtip whist downwind. With an increasing sensitivity to noise, aerodromes publish local circuit patterns as a single line on a map and then expect all pilots to follow the line. The line itself has been drawn on the basis of where the complainers live and hence places to avoid, nothing to do with where an aircraft actually goes if flying a circuit properly.
Too many instructors rush their students into the circuit, their comfort zone for teaching, and the poor student needs thinking time, so the circuit grows to accommodate this. Instead of going around if the aircraft in front extends, the next pilot extends further until the circuit leaves the ATZ!
As for 15 degrees of bank in a turn, often this emanates from the CFI and the poor instructor is just doing what he has been told. I recall one school where nobody was allowed to use full flap in case they have to go around!
Sadly, this nonsense gets worse rather than better