Go to the DT site:
https://www.dtswiss.com/en/component...ipples/nipples There are several variables when ordering the standard DT spokes: 4 lengths, 2 materials, 2 thread sizes, 2 colors.
I believe the guy you talked to is wrong; what would a 14 size hole look like, it sure would not be 14 mm. I think it is the length. Brass spoke nipples go on smoothly when a lubricant is used. I'd check spoke thread with nipple compatibility. I'd start over again with the correct size nipples.