Hi Mark!
/*
Theme Name: Twenty Fifteen Child
Theme URI: https://example.com/twenty-fifteen-child/
Description: Twenty Fifteen Child Theme
Author: John Doe
Author URI: https://example.com
Template: twentyfifteen
Version: 1.0.0
License: GNU General Public License v2 or later
License URI: https://www.gnu.org/licenses/gpl-2.0.html
Tags: light, dark, two-columns, right-sidebar, responsive-layout, accessibility-ready
Text Domain: twenty-fifteen-child
*/
Make sure you fill this out at the top of your child theme. The most important one is the template. I dont see you have that filled out in your examples so make sure the parents theme name is in that spot.You can also refer to the codex.