iPhone 15 Pro will rely on a titanium frame instead of stainless steel, and that should make for a noticeably lighter device. How much lighter are we talking?
iPhone 12, 13, and 14 all have similar size and shapes to iPhone 12 Pro, 13 Pro, and 14 Pro. The difference in aluminum versus stainless steel frames, however contributes to about an ounce of weight difference.
It’s something people notice in iPhone reviews. After handling an iPhone 14 Pro, the same sized iPhone 14 will feel like a hollow shell in comparison. Titanium still won’t make the iPhone Pro as light as aluminum models. It should lessen the gap though.