How much complex should model be?

I have trained the biGRU model for regression prediction. Currently I have pretty low train and eval loss at the 45 epoch. But I know that this is not the 100% prediction. So the question is should I make my model much more complex (e.g. to make stacked biGRU) to reach probably lower loss or it'd better to stop on this parameters?

Assumed the lowest loss is 0.028 or thereabouts

Whereas my loss at the 45 epoch is 0.034 (and it's almost the plateau)

But on the other hand I think that complexation can cause overfitting...

The target values are from 0.9 to 4.5