Well yeah, impedance dividers are out at DC.

Resistor divider will work as well as a linear regulator if your load is a constant 12V 2A, but if it varies, definitely big nah.
(Unless you argue that an SMPS is an impedance divider, in which case, sure!)
Traco is a pricey brand, are you sure you haven't found anything else?
The biggest thing to watch out for in buck converters, is the dropout voltage. Some can go to 100% duty cycle, some cannot. Check the datasheet.
The SMPS has higher efficiency, whereas the linear reg drops (15) - (12) = 3V and dissipates up to (3V) * (2A) = 6W. With a 24W load, evidently an SMPS below 83% is worse than useless; but a proper one should be well over 90%, which saves on power consumption, heat dissipation, size and overall cost (don't forget the cost of the heatsink, hardware, and labor in assembling them all together).
Tim