Display Disqus on front page of Twenty Fifteen theme

By adding a bit of code, Disqus can show on the front page of the Make and Me themes. Adding the same code to the Twenty Fifteen theme fails. Below is what I pasted in, followed by one difference I spotted in the themes in which the code works and the one in which it fails.

Any help you can provide this absolute novice would be deeply appreciated.

Thanks for taking the time.

Brian

…

<div id="disqus_thread"></div>
<script>
    /**
     *  RECOMMENDED CONFIGURATION VARIABLES: EDIT AND UNCOMMENT THE SECTION BELOW TO INSERT DYNAMIC VALUES FROM YOUR PLATFORM OR CMS.
     *  LEARN WHY DEFINING THESE VARIABLES IS IMPORTANT: https://disqus.com/admin/universalcode/#configuration-variables
     */
    /*
    var disqus_config = function () {
        this.page.url = PAGE_URL;  // Replace PAGE_URL with your page's canonical URL variable
        this.page.identifier = PAGE_IDENTIFIER; // Replace PAGE_IDENTIFIER with your page's unique identifier variable
    };
    */
    (function() {  // DON'T EDIT BELOW THIS LINE
        var d = document, s = d.createElement('script');

        s.src = '//thewafflesproject.disqus.com/embed.js';

        s.setAttribute('data-timestamp', +new Date());
        (d.head || d.body).appendChild(s);
    })();
</script>
<noscript>Please enable JavaScript to view the <a href="https://disqus.com/?ref_noscript" rel="nofollow">comments powered by Disqus.</a></noscript>

In the themes in which the code works, it comes right before this:

<?php endwhile; ?>

In the Twenty Fifteen theme, the code comes right before a different endwhile, one that looks like this:

// End the loop.
			endwhile;