Running an LDO (AMS1117) at maximum voltage
The datasheet absolute maximum input voltage is 15V. In general you do not operate with a nominal input equal to the absolute maximum. You don't even come close to the absolute maximum. 

Will a given unit break with 15.5V in? Probably not. Should you do it? no. Source a better regulator, dump voltage and power with a Zener or find some other way to keep well within the absolute maximum limits. 



Absolute maximum voltages are (usually) nothing to do with heat directly, they're more to do with sudden catastrophic failure when junctions break down because of a bit of a glitch on the power supply or whatever.