Optimisation problem (Load/Instantiate)

Hi, i'm coding a tile based map that load according to the player movement. I use a 3D map to easily handle complex physics. The 3D map consist of 9 chuncks around the player. Each chunk contains Mesh Collider of the landform. Then i would like to add tiles to give a 2D illusion. I'm having trouble trying to add tiles correctly. I did many tests but it's always very laggy. I tried to Instantiante the 256 chunk's tiles when it load, i also tried to preload every tiles and activate them when needed. What could be the best way to avoid that lag problem ?