Game FpS halve when TileMap is in viewport

I have a 200 * 100 TileMap with 16 * 16 tiles and generate it in “BeginPlay()”, as well as two layers. One layer is filled with one tile and the second one is filled with other tiles depending on PerlinNoise2D. “bCanEverTick” is set to wrong and nothing more happens in the class. I made a blueprint from the class. If I use this blueprint in the game and look at it in the game I see my nice generated TileMap as it should be, but the fps are halved and they double again when the TileMap is not in the game anymore.

Why does a measly 200 * 100 TileMap, which is not updated or does anything, halve the FpS?

And how can I improve the performance of the game when I look at the TileMap?