When I select Little Snitch Configuration (the rules) from the menubar icon it is really really slow before the window showing the rules is displayed. the app starts slow but not too bad (i.e. a blank menu bar with "Little Snitch Configuration" top left) but it takes an age for the rules list window to appear.
It was far far faster in v3 (i.e. always been slow under version 4). Running on rMBP 2.9 GHz Intel Core i7 macOS 10.12.6