How to wire a 12V DC fan to a Molex connection

Since DC motors are also generators, the reverse voltage raises proportional with the RPM. So the higher the RPM, the higher the reverse voltage -> less current. Also the ambient temperature is most probably not stable, which leads to fluctuating current measurement results.

For current draw, the peltier just looks like a resistor. However, as it heats up that resistance increases. So in order to get maximum current draw you need to keep it as cool as possible.

1.5 Amps still seems a little low, but these things are notorious for being specified poorly. All it really does is move heat, the end result being a temperature difference between the two sides. So the colder you keep the hot side, the colder the cold side will get.

Thermoelectric Cooling

The current is linear with supply voltage. If you supply a higher voltage you will get a proportionally larger current and the temperature difference between the two sides will increase(not proportionally though). If you exceed 80C or so on the hot side, your device will start to degrade. These are just rules of thumb not knowing your exact specifications.