From the sound of it, a significant part of the load is in heaters - that makes a big difference to the equation. For starters (no pun intended), the startup current of a motor anything like 18kW would be "quite considerable".
It may be worth a bit more investigation into the loads, and how the machine is wired.
1) Are the heaters needed all the time ? My guess is that it needs all the heaters while it's warming up, and then the heaters are modulated (either as a group, or in sequence) to maintain the required temperature. Depending on your requirements (duty cycle etc), it may be possible to disconnect one or more heaters at the expense of longer warm up time and/or lower duty cycles.
Regardless, the heaters are most likely 240V wired phase-neutral - and would be happy if you just wired the 3 input phase terminals to one phase.
2) Do the controls need 415V/3ph ? It's not uncommon for the controls to run from a single transformer - this may be 240V from one phase and neutral, or it may be 415V across 2 phases. If the latter, then replacing one transformer (and some rewiring) would get you controls that only need 1phase.
3) Having dealt with the heaters and controls, we are now left with the motor(s). Are these DOL or run from inverters ? What is the voltage on the motor rating plate ? If inverters are in use, and depending on the motor voltage, then it may be possible to replace the inverter with a different model to run from 1 phase. Or you may be able to run the motor(s) from a transformer/phase converter of an appropriately size for just the motor(s).
All this
may get you within range of running from a domestic supply
if your supply is large enough. It needs significantly more knowledge and electrical skills than you are likely to pick up by asking random questions here - and it's probably not going to be trivially cheap to do.
As an aside, at my last place they bought in machine (candle making machine) which was designed and procured by our US parent company. It arrived as a 380V/3phase/60Hz machine as the person designing and procuring it never thought about the supply being different. As it happened, the motors were either inverter driven, or not sensitive (50/60Hz rated) and driving non-speed-sensitive loads (fans). We had to buy a 'kin big transformer to run it from - when it could have been built as 415V just by selecting different devices from the same range at probably little difference in cost
