Updating AnkiDroid on B&N Nook

I have been using AnkiDroid on B&N Nook E-ink devices for over a decade. My current devices, two Nook Glowlight 3 (Android 4.4.2), have been in use with AnkiDroid for about three years. I’m a longtime supporter and donator to AnkiDroid, but had to stop monthly donations in June due to problems with my international credit card (should be resolved by December).

Today I tried to update to AnkiDroid 2.15.6 but it fails with INSTALL_FAILED_OLDER_SDK.

$ adb install -r AnkiDroid-2.15.6-universal.apk 
AnkiDroid-2.15.6-universal.apk: 1 file pushed. 1.3 MB/s (40131079 bytes in 30.492s)
        pkg: /data/local/tmp/AnkiDroid-2.15.6-universal.apk

What must be done to support these terrific E-Ink devices that I’ve been using for years without issue?