Sort taxonomies shown in the menu

Hello,

I am able to limit the number of taxonomies in my menu, however I also want to sort them by number of posts in it.

Here is the example: http://firm-guide.com/cars-manufacturer/audi/
In the submenu, there are 14 items (Abarth-Fiat), but they are sorted alphabetically. I want to show only those 14 with the most articles.

Here is the current template code:

$primary_taxonomy = $minisite->get_primary_taxonomy();
                                $terms = get_terms($primary_taxonomy->slug, array('parent' => 0, 'hide_empty' => 0, 'number' => 14));

Can we somehow implement sortby=number of posts?