Your FBX 3D model is too heavy primarily due to high polygon counts, unoptimized textures, or embedded unnecessary data (e.g., hidden objects, redundant animations).
High polygons add unneeded detail—like a simple prop with millions of faces instead of a few thousand. Unoptimized textures mean large, uncompressed files (e.g., 4K when 1K works). Embedded data includes unused animations, hidden layers, or extra metadata you don’t need.
To shrink its size, use free tools like Blender to decimate polygons, compress textures to PNG/JPG, and delete unused elements before exporting the FBX.