The purpose of the experiment is to measure time interval and not any precise reading. Hence, it does not matter whether the clocks that are compared to are showing correct time or not. What matters is that the clock is precise in measuring a particular time or not.
Clock 1: The time measured is 12:00. So, we will check how much the time varies around 12.
Clock 2: The time measured is 11:15. So, we will check how much the time varies around 11:15.
For clock 1: The least time measured is 11:59:04 which is 56 seconds off and the maximum time measured is 12:02:19 which is 139 seconds off. Hence, the time interval is 139+56=195 seconds.
For clock 2: The least time measured is 11:14:58 which is 2 seconds off and the maximum time measured is 11:15:24 which is 24 seconds off. Hence, the time interval is 2+24=26 seconds.
So, judging by the time interval measured, we can conclude that clock 2 should be preferred for the experiment.