0.15 B+F is not unusual. Could be light leak "due to handling". But it is something you could improve if that's the case.

The 5.5 minute test is overexposed, because you didn't "capture the toe" but notice how the curve continues all the way into your steps 20-30. Your other tests in the screenshot were camera tests and they are flat after step 20... The continuation of the curve in all steps of the test are what makes it clear to me that you made a contact exposure for the 5.5 minute test.