Calvin ✨

If your asset is already unwrapped with no overlapping shells, switch off "generate shadow maps" and switch shadow map channel to 0. It will reuse the unwrap you have made, saving memory.

If you have a complex character with lots of things like mesh buckles, laces, eyeballs, eyelashes and straps that don't change the silhouette, consider making a shadow casting proxy mesh. This is a simplified model with "hidden shadow" turned on ...(cont)

... the real mesh casts no shadows, the shadow proxy casts shadows but is hidden in game. A shadow has to be rendered, and the proxy renders way faster.

In maya, I split the screen into two viewports both with perspective view. One has "use scene lights" turned on to make the mesh go black. The other is the default lit mesh. This lets me see the silhouette- and what the shadow would look like

Rather than model hundreds of strips of transparent hair, consider modelling the solid bulk of the hair onto the head mesh, and lay a few strips over it to give the illusion of depth and strands. This greatly reduces overdraw.

Keep interior mouth geo super simple. Teeth and tongue can be separate floating meshes inside the mouth, the rest can be a simple blacked out box.

Your cut scene mesh where the character is talking and your gameplay mesh can be seperate LODs. Switching down shader complexity and bone count. For example, you may not need each finger rigged seperately during play, but they need to gesture, use keypads and dial in cuts

Bake/paint an eye into the texture inside of your models eye sockets. Delete the real eyeball in an early LOD- the auto LOD will pull out the eyelid mesh but the result will still render a face which appears to have eyes (at a distance, obviously).