Yeah, I just did a search and found there are indeed 15mm tubing and fittings available. That size appears to be skipped over by most hydraulic manufacturers I've used, like I said they seem to jump from 12 to 16mm, but it does exist.
I live not far from New Holland PA, and just assumed all of their tractors were made there, and would thus use Imperial-sized hydraulics. So I was more suggesting that it might be an inch size line, although 19/32" is even less common than 15mm, and I doubt there's enough paint in there to make a 9/16" line measure so large as .5925.
Doesn't New Holland have an online parts catalog, from which you can find/source these components? Deere has every part for damn near every machine they've ever made in their online parts catalogs. Go to catalog, type in machine or implement model number, and drill down thru the drawings to the part you need. That would tell you the fitting type at least, whether swagelok, ORFS, JIC, etc.