Why not just pull out the receptacle and see what gauge wiring it is running?
But yeah, what you could do is have one element running to your control panel, controlled via PID; then your other element plugged directly into the wall (or to your panel with a flip-receptacle combo) that's strictly on-off. That'd be the simplest route. There's also a way to have the PID control two elements simultaneously, I know PJ made a diagram for someone doing that... I think it's in that dual 2kw thread here on the front or second page.
But most importantly: you don't need to do any of this, most likely. People say 2000W will bring 5 gallons to a good boil, and some say it brings 6g to a boil, some say it doesnt (might depend on diameter and insulation?). So if 2000w boils 5+gal I don't see why 1500w wouldn't boil 3.25g fine?
I'm sure I could pull the outlet and check the gauge, but according to the box, it's a multi-outlet series - according to code (if I'm understanding it correctly) the 20A circuit has to be a dedicated circuit, which won't be possible with the current wiring in the walls.
I've been collecting PJ's diagrams - he makes wiring those controllers so easy. Seriously, I look at schematics all day long for work and his diagrams are purposeful, simple to understand, and easy to replicate even for those not electrically inclined. Dude needs a high five and a beer whenever he is met in society.
I think the only main issues I was concerned with when using the 1500W element was the time to boil and the level of uncertainty when using "enough" power instead of "MORE" power. I didn't know folks were using a single 2KW element for 5gal, I thought for sure that'd be in 3KW (208/220) or dual 2KW elements.
I'll plan the build with one 1500W element, but position the pickup tube and temp probe out of the way in case I need to add another element directly opposite the first.
Two other questions not directly related -
1) Sight glass for volume. Worth it? Or an additional "meh" to clean?
2) Anyone see the PID/SSR/heatsink combo on Amazon? LINK:
http://www.amazon.com/dp/B0087O6S2A/?tag=skimlinks_replacement-20
35 bucks seems a little cheap, but a 25A SSR and controller would fit the 1500W build with no issues I can see...