Speeding up render times is actually quite easy if you remember that everything you add has to be calculated.

I see some adding nodes and nodes and nodes, but remember. . . . . Everything you add has to be calculated.

Same goes for polycount, number of material zones, number and size of textures, number and type of lights.

And if you use the "modern" PBR workflow with older content, please remove all old "cheating nodes" when it is render time.

Many have proved that all content renders pretty good with very few nodes.

Less calculations to perform, and avoiding contradicting calculations speeds renders up.

In the end? Each rendered pixel has just a single R,G,B, value, and the pixel does not care where that came from.