You can't change the instantaneous current draw of a heater element on the mains, as its just resistive, you can only turn it on and off (at various rates). But at some point you will be overloading the mains circuit - which you should never do due to the risk to life and limb this poses through fire.
The only way that this could be made to work safely is by using a large autotransformer to dial down the voltage to the oven. Or the equivalent using
an electronic power-convertor. But would the oven even work in that condition, if it has control electronics it might be fussy about running at reduced voltage. Or even dangerous (some electrical appliances are unsafe on reduced voltage, like fridge motors which can stall during a brown-out and overheat - this is why permissable brown-out duration is limited by regulations).
Trying to flout the regulations on mains and mains wiring is a route to disaster.