Nothing impacts performance quite like the heat.
As with Austria and Frankfurt temperatures in Zurich were high and consequently age group times were slow. The 2015 median splits for swim, bike and run are almost universally slower than for the previous 10 years of racing. High temperatures impair performance right from the start when it’s a non-wetsuit swim. Clearly all age groups and the pros struggled more than usual under race day conditions.
Looking at split distributions emphasizes the changes in results. The non-wetsuit swim is significantly slower than usual, a relatively small percentage of the field duck under the hour mark. Bike and run follow with similar drop off in times from the front to the back of the field. Overall, the impact looks to be in the order of 20 minutes at the front of the age group race and closer to the hour from the middle back.