This is confirmed in tvOS firmware
Apple added references to iPhone15.4, iPhone15.5, iPhone16.1, and iPhone16.2 to the first beta of tvOS 17, and they lingered for a few betas before Apple noticed and removed them in beta #5.
The numbering is consistent with rumors that Apple will use the 3nm Apple A17 Bionic chip for the iPhone 15 Pro and Pro Max, while the iPhone 15 and 15 Plus will get the same Apple A16 chip used in the iPhone 14 Pro and Pro Max.
The latest Apple A17 Bionic will only get the iPhone 15 Pro and Pro Max
The 15.4 and 15.5 are in the same lineup as the iPhone 14 Pro and Pro Max, which were called iPhone15.2 and iPhone15.3, respectively. Apple uses the number “15” to refer to devices with the Apple A16 chip. And the iPhone 14 and iPhone 14 Plus smartphones are iPhone14.7 and iPhone14.8 because they use the Apple A15.
According to rumors, Apple plans to introduce new iPhone models on September 12, and sales will start on September 22.
