Theorytical your calculation may seem support single phase.
In practical, do all your electric use and on at same time to cause power overload ?
If you has heavy power usage but not all use at same time, then single phase is enough for it.
My house got 3 fridges, 4 unit 1hp air cond and 1 unit 2.5hp air cond. On daylight we just on the fridge and at night
only 2~3 air cond will use. Sometime will cause electric trip. For average monthly bill is RM300+
Almost every 1 years+ need ask technician to come my house to check on compressor of air cond and fridge because it not function.
After that change into 3 phase, the electric bill gone down about 20%.
My fridge and air cond now no need always call technician to check within 2 years.

If your house power usage is more then single phase supply then it will drain more power

It is cause by the wiring that you overload it. You still can achieve lower bill by rewiring your house with a single phase. And limit your appliccance to 1 power point.

When your appliccance draw high watt, wire will heat up and give resistance to the voltage (voltage drop). That draw higher amp to run your applicance. And longer the distance wire, resistance is higher. Another is wire material. Use this fomula -> V / R =I 

To counter this, Use bigger dia wire and plan your house wiring system properly. Some forunner here have some good wiring plan you might search back.

Let me give u illustration on that,
Imagine a train A pulling 1 passenger box which can carry 30 ppls.
While another train B pulling 3 passenger box which can carry 90 ppls with 30 passenger each box.

Now, if there is 60 ppls wanted to enter train A, then the box maybe fit for all 60 ppls but the situation will be crowded and will hot.

If that 60 ppls split and move to train B with 20 ppls each passenger box. Then it still normal situation .

If you load still below the limit of train A, then you can choose to enter train A. Else it will be train B.