Trying to understand Peltier module specification
This is a somewhat poorly written spec, but I think it's trying to say that you should aim to operate the Peltier at 12 V, at which point it will draw 5 A.  The maximum specs are what you should never exceed or the device could be damaged.

It seems these specs are meant for running from a 12 V lead acid battery, with some operating margin above reasonable charging voltage.  It's not clear whether 12 V or 15.4 V is the maximum cooling point.  However, it is clear you should design the power supply for 12 V nominal operation, it's OK if it occasionally goes a bit higher, but never over 15.4 V.