I think you just need to practice more or…
share scene with issues exposed and easily reproducible.
These are simple sets rendered using two different engines but same/similar technique (SPPM)
It’s Corona & LuxCore.
BTW Care to strip down your scene, isolate it to only what’s needed to expose an issue… or render until it clears. Because it might just be a hard case to solve/compute (image would also be noisy even when taking a photo w/o relying on tricks, SFX & post) or there are some unnatural values/settings in play… idk. Basically it comes down to what’s in detail - devil & god 
Then it’s not so uncommon for making such photo/image for hours or rendering for days.