There are long response times, which are a result of increased TTFB on requests from more complex category trees.
The CategoryList Widget will need a redesign to better accommodate larger more complete trees.
This is to be added as an enhancement in a future release of the product. The change will be to the CategoryList widget so that when it is presented with a large category tree it will not download it.
There is no current workaround at this time until that enhancement is released.