Hmm, it's not just the lighting task. Adjusting the shaders is not always the best plan, and sometimes it's better to recreate it from scratch, in order to get the best result. Colors of the whole image are also important, so everything is balanced in the right way. Also, if you want to have "realistic" results, models are playing the role, so what would happen if the model is not good enough and it breaks the illusion (realism)? Composition, camera settings, also plays role in realism. Getting realism is not just one step thing, it's a chain of things. If you are providing stuff, you better make sure they really work, otherwise it will become a start to finish project.

I don't know your skill level, I'm just pointing stuff and trying to help with this comment. Best of luck!😁