This reminds me of microcity which is a Simcity Clone for the Game Boy Colour.
The author has some great in-depth docs about the design, and how they managed to make a fairly lively-seeming simulation fit into a machine with an 8 MHz 8-bit processor.
https://github.com/AntonioND/ucity/blob/master/docs/index.rs...
Bear in mind that the GBC is almost between high end NES graphics and SNES.
That's my game! :)
I eventually ported it to the GBA, this time in C. It's essentially the same game, but with code that is easier to read. It's much less impressive in this case, there's even a version of SimCity 2000 for GBA that is much better than my game.
https://codeberg.org/SkyLyrac/ucity-advance