iOS update please

The iPhone 6s and 6s Plus are compatible with the current iOS 15 when an update is done over Wi-Fi, but one needs an iPhone 8 or later to upgrade to iOS 16 when it is released later this year.

Apple is not here in these public user-supported communities, so why questions regarding Apple business and product decisions cannot be answered.

iPhone 6 and iPhone 6 Plus are eight years old, and lack the hardware necessary for running newer iOS versions.

Newer hardware is substantially more capable, and substantially faster, and newer software is written for the newer hardware.

As one example of the hardware, iPhone 6 has half the memory of the oldest iPhone still supported by iOS 15, the iPhone 6s.

Google can still choose to support their apps on older versions of iOS; with iOS 12, in this case. They did not.

You will have to use the Google websites, pending a newer (used, refurb) or new iPhone.

At present, I would not recommend an iPhone older than iPhone 8. This is the minimum for iOS 16.