Active accessibility can be very slow - this is due the underlying size of the application model. If you image Blue Prism trawling through an enormouse tree veiw with evey element in the entire application, that will give you an idea why it can be slow.
To speed up the interface, as mentioned by Peter, you should always use Match Index with AA - and experiment to see if Match Reverse being ticked also helps. Match index means that once the element is found Blue Prism stops trawling through the rest of the model looking for duplicates.
Other hints for AA include: Untick as many elements as possible, including most of the Parent ones. Tick the Invisible attribute (it seems to work wheras visible and screen visible seem to do nothing). If you are having trouble identifying an element than the Application Navigator option in the identify button could be tried, but it can sometimes take a very long time to build the model tree.