I'll buck the current here... For interior shots, I'd stay away from the Ultra-wides.
It is correct that you can easily correct for barrel/pincushion distortion in post. Even for some tilt (you will find that your lens axis better be exactly perpendicular to the verticals and select horizontals, otherwise you get converging lines that ought to be parallel). Here is an extreme case:
There is a distortion (I don't know if there is another term) I'll call perspective distortion which no program can cure. It arises from the fact that the UWA covers... extreme angles. Say you are shooting a room interior. The wall opposite to you is say, 20 ft away. At your right, there is a chair at 3 ft. The Samyang on a tripod with the lens axis perfectly horizontal and perpendicular to the far wall will record a photo which is sharp all over, the walls are perfectly vertical and parallel, ...and the chair looks like a sofa!
You can't fix this in post. It is the projection of a 3D arrangement of objects to a 2D focal plane.
Here is a crude (handheld test of my Sigma 8-16, probably the third photo I shot with the lens)
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To the right it is an armchair, not a loveseat.
What I am trying to say, is don't fall in love with the short focal length. Make sure you buy the right tool for the job.
I've heard people having good results by stitching panoramas, rather than resorting to UUWA for interiors.