We are on the last legs with macOS Catalina. I installed the 10.15.6 Beta 1 on my Developer SSD today. It installed fine and my normal workflow Apps all work well, they are very snappy. Of course, when I get the 10.15.6 version of the OS to my main install it will slow down a bit because of all the stuff I have installed on my machine. I am sure the 10.15.6 version of Catalina will be the last based on what Apple has done over the past few years. I will continue to test and report back.