Touchwiz has slow transition speed. You can increase the transition speed.
In all the back and forth, most set lower speeds to reduce battery drain. I had almost forgotten about the setting. Well spotted.
The S6 was loading the web-pages faster than the iPhone 6.
You can check if the page is still loading on the iPhone by the top left side of the UI. There's a circle-ish shape there.
Transition speeds can be changed.
App loading speeds are even between the S6 and the iPhone 6, with the S6 being ahead by a small margin. Really, you're just nit-picking at this point.
https://www.youtube.com/watch?v=lsViP9LIrN0
As a sidenote, the S6 has a complete lead when going from app to homescreen. That is undeniable.