Here is more information on this weird saga with WiFi speeds.
Yesterday when I had issues, the tests on the MacBook, iPad and iPhone were done in the same location just minutes apart. The tests were done multiple times with effectively the same results. The iPhone struggled to get above 100 Mbps while the other devices happily cruised at speeds above 500 Mbps.
That indicates it is not an ISP problem. Nor is it a problem with the WiFi as far as the other devices are concerned. There may be some oddball setting that affects only the iPhone (160 MHz channel width on the 5G band?). I did reboot the entire AIMesh network, more than once just to eliminate the possibilities of a network reboot issue last night.
Today, I decided to remove the 160 MHz channel width from the 5G channels without changing anything else. The iPhone speed is back above 500 MHz. About the same as the other Apple devices on the network.
I then turned on the 160 MHz channel width, rebooted the network, forgot the WiFi network on the phone, and reconnected. Speeds were again down into the sub 100 Mbps range, sometimes dismally slow.
I turned off the 160 MHz channel width, rebooted the network, forgot the WiFi network on the phone, and reconnected. Speeds were back up to 500 Mbps +, about what I was getting earlier.
It would seem that the use of the 160 MHz channel width is causing the problem on the 5G WiFi network side. I also wonder if the Speedtest servers are playing some role as the iPhone 15 is being identified by the Speedtest app as being an iPhone 16.
Regardless, for those experiencing slow speeds on WiFi with iPhone 15, consider removing the 160 MHz channel width from the 5G network. While not an ideal solution it does seem to work. Apple borked something in the IOS 17.1 (Beta) update or borked something in the iPhone with IOS 17. Apple needs to fix the problem.
