Plain iPhone 15 models labeled as D3y will continue to use the WiFi 6 standard instead of WiFi 6E. D7x refers to the iPhone 14 Pro series, while D2y refers to the iPhone 14 and 14 Plus. The document cites antenna design changes between the iPhone 14 Pro and iPhone 15 Pro. Additional documentation is also available showing that WiFi 6E connectivity will be a Pro-only feature.
The document comes from the name who previously shared information about devices such as iPhone 14, accessed the copy before iOS 14 was released and shared details about the update. The document also confirms that the iPhone 15 Pro models will feature a faster 3nm A17 processor, redesigned volume and power buttons.