2/1.5 - 1.33, meaning the resistive element is using about 33% more juice to heat your water. The reported efficiencies are 72 and 84% for resistive and induction respectively, or 84/72 = 1.16.
I'm not sure why your shoot-out came out so much more efficient for the induction device, but container coverage of the heating element and a flat contact surface affect heat transfer.
Ignoring the container, the water took up 88 * 900 * 4.2 = 332640 Joules = 0.0924 kwh. This works out to 66% efficiency for the better induction device, and 46% for the resistive device.
Conclusions: if hot water is really what you want, an immersion heater in a container with low heat capacity has advantages. That actually is true for my home where we drink a lot of hot fluids and cook in the pressure cooker. My choice will be to buy a good thermos that I heat 1.5 liters of water in to boiling every AM and use through the day. I figure that should keep my electric consumption for hot water to something under 200 Wh a day. It will also let me use the pressure cooker for longer into the summer season since very little heat will escape inside the home (cooling down phase outside.)
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