I think that the best thing to is to try it and see if the results are acceptable for you. My comments above about diffraction were meant to be general and not specific to wider lenses. As I mentioned, I'd probably have attempted that shot at a wider aperture unless a slower shutter speed was what I was aiming for and for that reason going with a smaller aperture.
Back when I had Canon APS-C and FF cameras I had 50mm and 150mm macro lenses and they're the ones I used to stop down most. These days I have FF and MFT mirrorless and often use a 50mm macro stopped down or indeed sometimes other lenses but usually longer than 20mm.
To be honest I can't remember ever using wide lenses at small apertures for anything other than shutter speed (getting a slow one) as there's usually no need to stop down that far for depth of field.
Generally though I think that for me diffraction is mostly a non issue
for me and usually overcome to my satisfaction by moving the contrast and saturation sliders about in CS5