How to assign custom post template to its custom taxonomy terms

You should call your file taxonomy-interview_category.php to be automatically associated with your custom taxonomy.

If you want it to look like interview archive, you can just include archive-interview.php in your newly created taxonomy-interview_category.php.

I suggest you have a look at this image that explains WordPress template hierarchy and logic:

http://codex.wordpress.org/images/9/96/wp-template-hierarchy.jpg

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