I also use Nitrogen to generate 16 K maps. I have a Ryzen 7 2700X with 32GB, running Linux. It generates in less than 45 minutes and the generation process doesn't really use that much memory - 12GB or so, and the parms you pass to java will let it use more or less memory. It is not, however, very efficiently multi-threaded. Neither is vanilla RWG generation. If they put some serious multi threading in it, it could run 5-10 times faster.
Damocles did an amazing job on Nitrogen. My players love the worlds, the biomes and layout are amazing, and there are a lot of options for things like cities/towns amount and size, rivers, small/large lakes. It is everything vanilla RWG should have been, and more. TFP has a tough act to follow. They put the potential into RWG, but they have not taken advantage of it.