Very long generation time building flat map for stamping 158x158 tiles with tile size 128

[nhunter]

Our team building big openworld game. Firstly, we generated 40x40 tiles with size of 1024. Each scene contained trees, grass etc. And in runtime we find that Unity's async, additive scene loading produces freeze for 30 secs. So we decided to split our 1600 sqr km map to tiles with size 128. Since Gaia has bug of blending small tiles in big worlds, we decided to generate flat map (maybe it will be faster). So I launched generation of 158x158 tiles with tile size of 128m, "world generation for stamp". And it takes 11 days!!! PC specs: AMD Ryzen 7 3800X, 128 GB of RAM, no GPU(on PC with GPU it takes more time, since cpu is lower than dedicated machine). Unity task is set to High priority. Can somebody tell me how to generate 158x158 chunks with chunk size of 128m, faster?

[nhunter]

for 312x312 tiles with tile size of 128, it takes 24 days😱