There's already a Final Fantasy XV mod that optimises performance

Final Fantasy XV on PC has received its first stability mod, courtesy of Steam modder “Kaldaien”.

Here’s why the PC version of Final Fantasy XV is the best version.

According to DSOGaming, Kaldaien has turned their magic optimising fingers to Final Fantasy XV, improving the game’s stability, reducing its issues with stuttering (something Matt discovered when working on his tech review), and increasing startup performance.

from
https://www.pcgamesn.com/final-fantasy-xv/final-fantasy-xv-stability-mod