What number should replace the question mark in the series given below? 15, 15, 22.5, 45, 112.5, 337.5, ?

The next term is 1181.25.

The multiplier grows by 0.5 each step: x1, x1.5, x2, x2.5, x3, x3.5.

15 x 1 = 15, 15 x 1.5 = 22.5, 22.5 x 2 = 45.

45 x 2.5 = 112.5, 112.5 x 3 = 337.5.

337.5 x 3.5 = 1181.25.

Method: multiplier increases by 0.5 each time.