hello, youccan use unity terrain, go to settings and adjust some parameter like high map resolution, detail resolution, detail resolution per patch etc.
please see the documentation firs because heigh map resolution needs to be power of two +1.
i run unity terrains on huawei Y9 on 60 fps.
when i you are noob on unity is too dificult find this information, please consider make me a small donation :) . thanks !