This sort of stuff has been discussed to death in the heatstick thread.
1500W won't get the job done for you. 2000W will get it done very slowly.... like.... 2 hours to get your boil started if it can even manage to do it at all.
Folks using the 120V/2000W heatsticks seem to be using 2 of them (4000W total) to get 6 gallons boiling and then turn one off an maintain that boil with 2000W.
Ground Fault Brewing Co.