From my understanding, number of threads configurable are linked to number of virtuoso connections.
If I have 32 threads and 1500 jobs, I would expect that 32 jobs run concurrently, and batches within the job runs sequentially.
I think that could make a better usage of resources.
e.g:
job number 1 has 11 batches => seems that 21 threads doesn't do anything during that time (could run other jobs but doesn't seem so)