these problems are most likely media quality errors. burnt media is nowhere near as good of quality as pressed media no matter what brand you use. the only thing i can suggest you to try is clean your laser, and try lowering the speed of your drive to 8x or 5x if 8x doesnt improve it.
yes, lower speeds will decrease read times. but as the game uses alot of disc activity with the laser going back and forth all the time, (heres my theory) the laser may be receiving errors as its reading a sector, and comes round again to read it untill it fully reads the sector which causes the texture to take a while to load. by lowering the drives speed, you will increase the lasers accuracy with its reading which means it may not have to come round for a second or third read of each sector, and will cause the textures to load sooner. that is if my theory is correct.