[Plugin: NextGEN Gallery] Gallery files on subdomain

Well, it’s possible to make this without changes in NextGEN:

function SE_gallery_filter_content( $content ) {
  if (strpos($content, "https://www.domain.de/wp-content/gallery") !== FALSE) {
		$content = str_replace('https://www.domain.de/wp-content/gallery', 'https://media.domain.de', $content);
  };
  return $content;
};

add_filter('the_content', 'se_gallery_filter_content', 100);

=> The subdomain media.domain.de points directly on https://www.domain.de/wp-content/gallery. The code above only replaces the normal url (https://www.domain.de/wp-content/gallery/…) by the new subdomain-url (https://media.domain.de/…).

But this is not a good solution, because it will slow down wordpress!

I have the same problem. Better solution?