View with relationship - column displaying count of related nodes
You can do this with Aggregation. 

First create your normal Views listing Interviewee nodes. Add the Media reference field and set to show all values in one row. 

Turn Aggregation on, and change the Aggregation settings for the Media reference field to Count or Count DISTINCT. 

Sorting criteria can sometimes mess up Aggregation counting so it's best not to have any while you're configuring the Aggregation, then add later once you know Aggregation is working and check each step that it's working as expected. 

You can even add the Sort criteria for the reference field and use Aggregation on it (again Count or Count DISTINCT), Expose it if you want to allow users to change the order Ascending/Descending. 

Sorting also works in a table Format if you turn on sorting for that field.