This guide will help you downgrade to 15.x on an A12 with SHSH blobs.
This process relies on a small "loophole" in the way iOS activation works. Since 2022 it has long been documented that the SEP from iOS 16.x and newer have issues activating on iOS 14 and 15, making restoring to those versions largely impossible without playing with activation tickets (not to mention, it would not have been possible to get the tickets on versions newer than 17.0 due to the lack of a jailbreak, and restoring them would not have been possible because there is currently no usbliter8 based jailbreak). However, for some unknown (and frankly cursed) reason, iOS 14.0 Beta 4 seems to activate just fine with 18.x and 26.x SEP versions. We can take advantage of this and use it to update to 15.x since it does not need to go through the activation process again.
Note: This guide should work with 14.x blobs, but it has not been tested currently. iOS 12 and 13 will not work since they