A watt is a watt. A 1500 watt heater provides the same amount of heat as any other 1500 watt heater. However, an infrared heater can more easily be directed toward the occupants, heating them a little more without heating the room as much & can make it seem as if it's warmer (well, if there's only one occupant.) Then again, you can get a 1500 watt heat gun, or a blow dryer, and just aim it at yourself - same effect. But, over time, either will provide the same amount of heat to the room. Then again, the infrared heater, if aimed toward the wall, will heat the wall a little warmer than it otherwise would have been. Heat transfer is related to the difference in temperature, so a warmer wall is going to radiate more heat to the outside than a cooler wall.
That said, I'd then base my decision on which unit is safest to operate. Does it have a tip-over switch? Does it have exposed elements that are hot enough to set a piece of paper on fire (or accumulated dust)?