Since,the dawn of physics many path breaking researches have come into existence,but the theory of gravitational waves was a different one.
Gravitational waves was one of the theories developed by einstien but it was merely a prediction.The concept of spacetime was too absurd but it was predicted by mathematics and was convincing.
Gravitational waves-Gravitational waves are 'ripples' in the fabric of space-time caused by some of the most violent and energetic processes in the Universe.
Now lets come to your Question Of Speed.
the speed of gravitational wave is c ,that is ,Speed of light.
but what was experimentally found was a bit different but almost the same.
"As Jupiter moved between Earth and the quasar, the gravitational bending of Jupiter allowed us to measure the speed of gravity, ruling out an infinite speed and determining that the speed of gravity was between 2.55 × 10^8 and 3.81 × 10^8 meters-per-second, completely consistent with Einstein's predictions."