I just had a look at the tests that take longest to run and Jenkins reports that 13 minutes (out of the total of 53min) are spent in the frag6 tests. Looking at the python code there are lots of sleep(75) calls. Do these tests really need to sleep for 1m15s?
This was addressed by commit e32221a15f089282e5dfe18891c5312b26cbe3ba, the frag6 tests finish much more quickly now.