It depends what you've come from.
You went from a 4S to a 6 Plus, so you've skipped two generations of iPhone so have seen a pretty huge performance leap to you personally.
Normally the benchmarks and specs between the new iPhone and iPad are quite close, but Apple pushed the boat out with the Air 2. On Geekbench, and I know it's only benchmarks and not indicative of real world use, the iPhone 5s and 6/6Plus are very close in both single and multi core scores. Normally you see a near double the leap in performance numbers (like on the Air 2 with it's multi core score vs the Air 1).
I've heard a lot of people who've come from a 5s say that the 6 and 6 Plus are simply 'bigger screen versions of the iPhone 5s in a new body'. Performance wise there's very little between the 5s and 6, but the 6s SHOULD have some decent speed spec bumps.
Cannot and will not disagree, you're dead on.