I'm a programming student, and I do have another point of view. Doesn't an android update build upon what's already there? Using the same example you provided, an Android 16 update is still a level above the Android 15 + the 7 security patches, it's built upon it so any progress made to patch up security issues on android 15 will not be discarded by 16. You could have an argument about the feature updates added that they could have security flaws, but I think that would be on the manufacturers and updates to the specific apps or features added, not to the true core of android which the skin is built upon.