How to prevent Profile2 fields from loading on user registration?
Been struggling for quite some days now so if anyone has clues on how
  to prevent the loading of the whole profile form


Looks to me that the magic happens in profile2.module from line 436 to 460


/**
 * Implements hook_form_FORM_ID_alter() for the registration form.
 */
function profile2_form_user_register_form_alter(&amp;$form, &amp;$form_state) {
  foreach (profile2_get_types() as $type_name =&gt; $profile_type) {
    if (!empty($profile_type-&gt;data['registration'])) {
      if (empty($form_state['profiles'][$type_name])) {
        $form_state['profiles'][$type_name] = profile2_create(array('type' =&gt; $type_name));
      }
    }
  }

  // If we have profiles to attach to the registration form - then do it.
  if (!empty($form_state['profiles'])) {
    profile2_attach_form($form, $form_state);

    // Wrap each profile form in a fieldset.
    foreach ($form_state['profiles'] as $type_name =&gt; $profile_type) {
      $form['profile_' . $type_name] += array(
        '#type' =&gt; 'fieldset',
        '#title' =&gt; check_plain($profile_type-&gt;getTranslation('label')),
      );
    }
  }
}



Usually I would never hack a contrib module directly, but unfortunately here there is no other option considering you have a profile field that loads 30,000 terms. So comment this out and flush/clear cache. 

Just remember if there is ever an update to this module, it will override your changes, so you will have to comment it out again then.