title: Django admin increases response times
body: <p>I recently added an app to my Django web application. I am baffled at an issue that is occurring. When I add the below admin.py file to the app and deploy the code, response times increase in multiple areas of the site, with many areas unrelated. Is there something wrong about the way the ModelAdmin is written? Has anybody experienced this before? I am running Django 1.11.</p>
  
  <p>admin.py:</p>
  
  <pre><code>class SubscriberAdmin(admin.ModelAdmin):
      list_display = ('email',)
      fields = ('email', 'verified')
      readonly_fields = ('email', 'verified')
      list_per_page = 50
  
  
  admin.site.register(Subscriber, SubscriberAdmin)
  </code></pre>
  
  <p>models.py:</p>
  
  <pre><code>class Subscriber(models.Model):
      email = models.EmailField(null=False, unique=True)
      activation_key = models.CharField(max_length=64)
      key_expires = models.DateTimeField(default=get_key_expiration)
      verified = models.BooleanField(default=False)
  
      agency_class = {}
      agency_type = None
  
      @classmethod
      def send_notifications(cls, agency_type, slugs):
          """
          Sends notification emails to all subscribers.
          :param agency_type: 'salary' or 'pension'
          :param slugs: [list of agency slugs]
          """
          cls._set_agency_type(agency_type)
  
          subscribers = cls.objects.all()
          for subscriber in subscribers:
              subscriber._send_notification(slugs)
  
      def _send_notification(self, slugs):
           # code removed for brevity
  </code></pre>