Canon SX150 IS has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Digic 4 processor. On the other hand, Canon SX70 HS has a
20.0MP (1/2. ) sized BSI-CMOS sensor and features Digic 8 processor.
Canon SX70 HS's sensor provides 6MP more than Canon SX150 IS's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the SX150 IS and SX70 HS sensor size comparison.
As seen above, Canon SX150 IS has a infx Larger sensor area than Canon SX70 HS. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.