You probably do not want to use noise reduction in astrophotography because algorithms can think of stars as noise!
Generally, when you choose a lens for astrophotography, you want a short focal length and a large aperture simultaneously. You can calculate an "astrophotography index" for lenses, and this index should be as low as possible. The index is:
I = f * N2
where f is the focal length and N is the opening number. Example: The index is 141.12 for Zeiss and 80 for Tokina. So, you should get the Tokina because it captures 76.5% more light, so you can use 0.57 times the ISO you use for Zeiss. Lower ISO, less noise.
BTW, according to this index, the Samyang 14mm f / 2.8 is worse than Tokina 20mm f / 2.0.
More information: https://www.lonelyspeck.com/lenses-for-milky-way-photography/ – note however that their "ranking" (which should be high, not low) is calculated at the # 39, using a different formula so that numeric values are not comparable.
Justification of the index formula: opening opening in units of length squared (proportional to2/ NOT2) and the field of view in units of angle squared (proportional to 1 / f2) indicates how much you can collect light. However, the maximum exposure time is proportional to 1 / f because you do not want star trails; the light collection capacity is therefore proportional to 1 / (f * N2), you will want as high as possible 1 / (f * N2) or in other words as low as possible f * N2.