Interesting idea, I suspect it isn't possible with the existing connector. You either need to increase the voltage or the current.
The new 240W spec is 5A and 50V. Assuming 5A is the thermal limit of the connector and that can't change, to get 1500W you'd need 300V, which is probably higher than the connector can support in terms of conductor spacing.
Maybe you can get there if the device doesn’t actually require a steady stream of 1500W. For example, induction stovetops often work with cycling their coils. Couple the idea of a charge pump, a whole bank of capacitors and Tesla’s trick of running cables over spec by constantly monitoring temperature and making on-the-fly adjustments, and you might get somewhere.
You may be able to run cables 50-100% over spec for a short time. But not 1000%. Thought experiment (don't try at home!): Take a random USB cable and short circuit a car battery. It will start burning within seconds.
At uni we learned that 30V can penetrate skin in the right (wrong?) conditions. Once it's through the skin, your body conducts really well, so even a tiny amount of current can stop your heart. But you need a path for the current to get across your heart, so I'm guessing that even if 30V gets under your skin, you'd have to be pretty unlucky for it to form a circuit through your heart.
The new 240W spec is 5A and 50V. Assuming 5A is the thermal limit of the connector and that can't change, to get 1500W you'd need 300V, which is probably higher than the connector can support in terms of conductor spacing.