mesh render issue on andriod apk

i just made a simple terrain in my sene and then convert the terrain to obj becz unity terrain causes the frame drop issues on mobile device,the problem is that i can see that my terrain in obj format in my apk build any solution? i test it on my 2 device with 4gb ram and 2 GB ,the 4gb mobile render it properly but in my 2gb ram mobile it doesn't render and the sene remain empty