Quartersawn piece for bowl too heavy

Hi, I quartersawed a piece of yellowbox, and have got it down to about 15" in diameter, and 6" thick, with a roughly octagonal cylindrical shape,I have it on the faceplate, but when I mount it on the lathe and turn it on, it just about wants to throw the lathe across the room!

I don't have a bandsaw and am finding it difficult to shape it down, advice please?!