Here are all the new iOS 15 features that iPhone 6s, iPhone 7, iPhone 8, and iPhone X won't get, for the lack of an at least A12 Bionic chipset:
Home, office, hotel, car keys, and remote keyless entry controls: basically all the new Wallet app features are off-limits for older
iPhones.
Spatial audio during FaceTime: voices are spread out to sound like they’re coming from the direction in which they’re positioned on the call.
Portrait mode: portrait mode in FaceTime blurs your background and puts the focus on you.
Live Text and object recognition: interact with text and recognized objects or landmarks in live Camera previews, Photos, Screenshot, Quick Look, and Safari.
Fast on-device speech processing: faster Siri, offline Timers & Alarms, Phone, Messaging, Sharing, App Launch, Control Audio Playback, and Settings control.
Continuous on-device dictation.
Interactive globe: interactive 3D globe in Maps, with extra mountain ranges, deserts, forests, oceans, etc., details.
Immersive walking directions: step-by-step directions shown in augmented reality.
Detailed city experience in Maps: San Francisco, Los Angeles, New York, or London get high level of detail for roads, trees, buildings, or landmarks.
New animated backgrounds in the Weather app: reflecting the sun position, clouds, or precipitation.
Zoom in QuickTake video: swipe up or down while taking a QuickTake video to zoom in or out.