Canon ELPH 150 IS has a 20.0MP 1/2.3' (6.17 x 4.55 mm ) sized CCD sensor and features Digic 4+ processor. On the other hand, Olympus VH-515 has a 12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features TruePic III+ processor.
Canon ELPH 150 IS's sensor provides 8MP more than Olympus VH-515'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 ELPH 150 IS and VH-515 sensor size comparison.
Sensor Size and Resolution Comparison image of Canon ELPH 150 IS and Olympus VH-515 Cameras
Canon ELPH 150 IS and Olympus VH-515 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.