How should I set up a 2D game map?

Godot Version

Godot 4.22

Question

I’m a game developer and I’m using Godot to paint my dream game. It is a 2.5D game, my character is 8-way tile material, now I have a 4500 x 3000 pixel 16M JPG image.
I tried using TileMap to divide them into 16 × 16 tiles, but this made GoDot very slow, often unresponsive, stuck, and loaded with the mouse.
Can I directly put the whole picture into TileMap as a tile? Or just put the images into the game without TileMap?
Please tell me how the standard operation should be done!