Hi, there is not hard limitation, the only limitation that exists is by your computer memory and the amount you allow for openLCA. Also, in older versions (pre 1.6), the calculation was slower.
For 45 processes, it should not take long really. I assume you clicked on start when the MC simulation windows opens and has performed one calculation, see screenshot? Otherwise the simulation will not start and thus indeed take until eternity to finish..
Best
Andreas