Voltage divider on AC current?
Let's say you wanted to make a voltage divider that created 45V @ 15 amps output. Your resistor would have to handle the other 45V @ 15 amps. That's 675 Watts that a single resistor would have to handle. A kilowatt resistor runs somewhere around a couple hundred bucks. That's only for a single power setting. You'd want a variable kilowatt resistor. I'm not sure that even exists. If it does, it'd cost you even more. 

In summary, NO. It's a bad idea. You need a smarter power supply so that you're not having to dissipate so much energy directly as heat.