Ran at ~15-16 fps on my iPhone 17 air, horizontally (2211x1245) , for about a minute until my phone got ridiculously hot and thermal throttled down to 10-12fps.

To be fair you can optimize this a bunch if you put in the effort. Sphere tracing is far from optimal for ray marching.

edit: see https://hal.science/hal-05308455v1

SDF techniques are widely used in real games, even if a shadertoy put together in an hour or two doesn't run well on low spec hardware.