An electric kettle consumes around 1,200 watts of electricity per hour or while it's on and boiling water.
So yes an electric kettle does consume a lot of electricity.
However the electric kettle will only be on for a short amount of time and it should not raise your electricity bill by a lot.
I use an electric kettle nearly everyday and I mostly see my electric bill rise by around $3.00 per month when the electric kettle is being used.
So it's not all that expensive.
A kettle will boil water quicker when there is less water in the kettle.
When you have less water in the kettle it takes less time to boil the water in the kettle because there's less water needed to be heated up.
When you have more water in the kettle it takes a bit longer to bring the water in the kettle to the boiling point.
If you just want to make a little tea such as one or two cups of tea and you need to boil water then just fill the kettle halfway.
The kettle will boil the water faster than it would if the kettle was full of water.
A stove top kettle that you put on the stove to boil water will boil much faster than an electric kettle will.
But if you're using an electric kettle then fill it just enough to boil the amount of water you need so that it can also save electricity as well and heat the water much faster.