Precision shunt regulator failure behavior
The 15mA listed is the recommended operating condition. The absolute maximum given is 20mA, which is still well above the supposed current that was applied to the device. This means that the device will likely not last as long as would have been expected otherwise, but (as an example) 90% of 20 years is 18 years, still a decent lifetime.

Nonetheless, don't let this keep you from swapping out the device if you suspect that it has been damaged and is directly responsible for any issues.