Like others, I have had discussions with Bernie supporters in who do reject democratic processes.
One young person, for example, told me that the "party" should overrule the voters . . .
Then he showed me the numbers. A majority of young Democrats wanted Sanders, so if Sanders wasn't the nominee, it would prove . . .
I tried to explain to him that allowing the young people to choose would also be undemocratic. Everyone gets one vote, regardless of age.
He insisted that the "party" must come to its senses and nominate Sanders.
15% is a small percentage. But some do reject rules and processes.
See my thread yesterday on why people give up on democracy: It can be frustrating when we don't get our own way. An autocrat always gets his way.