Casio EX-ZR15 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor and features Exilim Engine 5.0 processor. On the other hand, Nikon D100 has a
6.0MP APS-C (23.7 x 15.5 mm ) sized CCD sensor .
Casio EX-ZR15's sensor provides 10MP more than Nikon D100'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 EX-ZR15 and D100 sensor size comparison.
As seen above, Nikon D100 has a 13.1x Larger sensor area than Casio EX-ZR15. 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.