Can I ‘order by’ date that is in a text field?

Your Problem isn’t that big. As your meta data is stored in the Y m D format, you should be able to just sort by it (I am going to assume that the format uses leading zeros).

You just add “meta_key” to your query arguments like this:

$args2 = array(
  'post_type' => 'joblist', 
  'post_status' => 'publish', 
  'showposts' => -1, 
  'order' => 'ASC',
  'meta_key' => 'completion_date', //change for the correct meta key
  'orderby' => 'meta_value_num'
);
$slider_loop2 = new WP_Query($args2);

Be aware: because WordPress uses an INNER JOIN to join the two tables, with this query there will be NO Posts, that do NOT possess this meta value. So if there are Posts that don’t have that value set, they will not be in your query.

Happy Coding!