That’s not surprising. The 11 uses an LCD and the 15 uses an OLED. So because the display technology is different they’re bound to be different from each other.

Normally this isn’t be a problem on Android’s because you can adjust the display warmth to your tastes. Unfortunately, because iPhones use True Tone; the hardware/Software adjusts the warmth of your display. Theoretically with True Tone enabled, both the 11 and 15 should be close in terms of warmth. Unfortunately that may not necessarily be to your taste.

One to two. Typically keep my phone 4 years.

Zero likelihood; because:

1. Apple is a bunch of control freaks.

2. Apple doesn’t have the programming chops to figure out how to do it.

Take your pick.

Zero!