Here I guess that you expect your tests in parallel mode to run faster than in sequential mode.
In my humble opinion, the parallel mode of Test Suite Collection runs no faster than the sequential mode. So the parallel mode is not really usefull. Why? See the following post of mine.
and
I would suggest you:
Don’t use a Test Suite Collection at all
Create multiple Test Suites. Let CI/CD pipeline to distributes the Test Suites into multiple agents on mutilple machines; as an extreme case, let a single Test Suite to run on a single box.
You need to purchase multiple KRE licenses; the number of licenses will be equal to or greater than the number of processes to which you distribute your Test Suites.