Both Sony WX500 and Sony WX150 have 18.0 MP resolution sensors but Sony WX500's sensor is 1/2.3 (6.17 x 4.55 mm ) and Sony WX150's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Sony WX150's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Sony WX500.
Below you can see the WX500 and WX150 sensor size comparison.
Sony WX500 and Sony WX150 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.