Thinking logically setting perspective wallpaper requires some constant recalculations of background position. When I hold my iPhone and move hand, I see that effect. It's nice and pleases the eye but I'm sure that it requires some CPU calculations and that triggers higher energy consumption since nothing's for free…
Question is - how much energy is consumed by this setting over still and can this have a significant impact on battery life in a longer time perspective?
Whilst it would reduce battery as its constantly using sensor data and updating the display it doesn't (in my experience) reduce the battery noticeably, however on older devices it does cause some FPS issue, in which case reduce motion is recommended as well as a still background image.
"Low Power Mode" (in the Battery settings) says that some visual effects are reduced or turned off. I have most of the distractions turned off by default, so I don't know if the perspective effect is one of the ones which is turned off in low power mode. But even if Apple feels that it does have a calculable effect, it is probably not noticeable over the course of a normal charge cycle.