Leica TL has a 16.0MP APS-C (23.6 x 15.7 mm ) sized CMOS sensor . On the other hand, Leica TL2 has a 24.0MP APS-C (23.6 x 15.7 mm ) sized CMOS sensor .
Leica TL2's sensor provides 8MP more than Leica TL'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 TL and sensor size comparison.
Leica TL and Leica TL2 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Leica TL has 50% larger pixel area compared to Leica TL2, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.