ICE MELTING?!?!?

Heat moves to cold, so if a cold thing is next to another cold thing at the same temperature, there won't be any heat movement. The only melting on that face will be where the (warmer) air manages to get in along cracks and gaps. It wouldn't be unusual for the two cubes to actually freeze into one when that bit of melt trickles down and fills a gap between the two cubes, actually.

So the two cubes will melt as if they are one of a longer shape.

Heat of fusion of water is 144 BTU to change one pound of water ice at 32F to one pound of liquid water at 32F. The bigger the ice cubes the more BTUs needed to melt them. The BTU (British Thermal Unit), Pound and Fahrenheit are not the Metric System and your teacher may chastise you for using the English System.

Slower. The surface area to volume ratio is lower, so the rate of heat transfer is lower.