Featured Gallery on home page loads really slowly

The featured gallery on the home page loads really slowly. The problem is that it uses the full image sizes instead of thumbnails.

I fixed it in on my site by editing one of the template files: photograph/page-templates/photograph-template.php

I changed line 122 to this:

<img src="<?php the_post_thumbnail_url('thumbnail'); ?>"/>

I then changed my default thumbnail size to 462 x 275 and then regenerated my sites thumbnails

Hopefully you can incorporate this into your theme.

Also, I tried submitting this as a support request on your site, but wordfence blocked me out.