First AJAX request is working very well, next takes too much time
I found a solution that's working for me.
I just changed that:

$('#content-region-inner').load(url, 'ajax=1', function () {
      Drupal.attachBehaviors('#content-region-inner');


into that:

var result = $('#content-region-inner:not(.my_ajax-processed)', context)
    .load(url,'ajax=1',function() {
               Drupal.attachBehaviors(result);  


When using that, Drupal only fires up Drupal.attachBehaviors() once a time, no matter how much requests you do.

I hope this is working for you, too