@inmarket Thanks for those points.
I was using ROMFS to read the file from internal flash. I saw the caching, but when I tried to use it it returned error, not enough ram. I read somewhere else here that the library is not using external ram for caching, but there is a workaround. I also read someone say that the performance difference between cached image and flash image is negligible. Eventually we will he reading map tiles from sdcard so it will need to be cached once loaded.
I'll look into building the project with full make.
Thanks for you help here, I will keep posting as I learn how to use this great library.