The default, with good visibility in ideal conditions, should be to not exceed the speed limit.
In a school zone, when in a situation of low visibility, the car should likely be going significantly below the speed limit.
So, it's not a case of 17mph vs 15mph, but more like 17mph vs 10mph or 5mph.
So let me get this straight, the car should have been going less than the speed limit, but the fact that it was going a hair over the speed limit is the problem?
The car clearly failed to identify that this was a situation it needed to be going slower. The fact that it was going 17 instead of 15 is basically irrelevant here except as fodder for moral posturing. If the car is incapable of identifying those situations no amount of "muh magic number on sign" is going to fix it. You'll just have the same exact accident again in a 20 school zone.
>The default, with good visibility in ideal conditions, should be to not exceed the speed limit.
Please pass this message on to 99.999% of human drivers who think speed limit is the minimum speed.