I do a lot of interior shots for architects and real estate folks and the 21 (at least the nikkor) has a bit more distortion than I like. Also, the 25 2.8 is far more affordable.
For interior shots, likely as not, they are not needed to be printed large. I'd consider something even wider or else designed for architecture like like the Canon 24mm T/S II. but you'd need the
Nikon version. Unfortunately, it appears that its tilt is not freely rotatable with respect to its shift and yes, it's heavy.
I use the 24mm TSE Canon Version II and it's one of the best lenses I own. I sold all my Nikon and soon this 24mm TSE will have its own adapter for the Zeiss A7r and I might sell off all my Canon gear.
Asher