Samsung Galaxy NX has a
20.0MP APS-C (23.5 x 15.7 mm ) sized CMOS sensor and features DRIMe IV processor. On the other hand, Samsung NX5 has a
15.0MP APS-C (23.4 x 15.6 mm ) sized CMOS sensor and features DRIM Engine processor.
Samsung Galaxy NX's sensor provides 5MP more than Samsung NX5'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 Galaxy NX and NX5 sensor size comparison.
Samsung Galaxy NX and Samsung NX5 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.