Thanks, @Evgeni_Popov!
That‘s better. Do you have an idea why it slows down faster than with normal render loop?
https://www.babylonjs-playground.com/#UNB24W#8
EDIT:
Setting the parameters for scene.render() seems to fix that problem: scene.render(false, true): https://www.babylonjs-playground.com/#UNB24W#10