Yeah, having such low end devices at one end of the spectrum would push Apple to make iOS 9 efficient, thus, greatly improving performance on all devices. However, because they have so many devices to test/develop for, it can complicate things.
My friend has a Galaxy S5 and the new lollipop update already uses around 1300MB out of 1.6GB (not sure why it said 1.6GB available when the device has 2GB of RAM?) I remember my Galaxy S4 had usually around 800MB of RAM being used on KitKat.
So, what one can take from this is since Samsung is growing so damn fast spec wise, it freaking ruins older devices and general OS quality. Her S5 was already stuttering a good amount, worse than my iPhone 6 and my mini 2. However, the mini 2 has much more heavy stuttering in some spots compared to the S5. Even so, the S5 had a consistent stutter over just about everything it felt like. They don't have to worry about how bloated their version of android is because they just keep chucking power at it. It just does not seem sustainable. At all.
Maybe she had a stuck process or something, I don't know. It was just generally stuttery... My experience.