Both Leica TL and Olympus E-PL8 have 16.0 MP resolution sensors but Leica TL's sensor is APS-C (23.6 x 15.7 mm ) and Olympus E-PL8's sensor is Four Thirds (17.3 x 13 mm ).
Since Leica TL'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 Olympus E-PL8.
Below you can see the TL and E-PL8 sensor size comparison.
As seen above, Leica TL has a 1.6x Larger sensor area than Olympus E-PL8. 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.