Very smooth operation of Premiere Pro beta

Dear all, I noticed a very smooth and faster working system in version 22.1 compared to version 15.4 . I am working on OS 10.5.7, quite recently moved from Mojave .

I am editing a 75 minute documentary film , I am also doing tests on beta  system
I work using Production tool , And it works much better with a large number of files , with mulicam files .
I try to be careful but somehow working on this version is a lot
better , no crashes at all.....  

Something is internally changed , the beta system does not work with the Mojave version ...
I am curious when this internal change will appear in the official version ?

And I have a question , how to open a project from beta version  on the official version ..PP.