congrats, nice one!.
as has been said a large chuck is a terrible all around choice.
besides the other reasons already laid out, it is also harder to zero work because the threads are very coarse on the screws,
those honkin big jaws swingin around at 1000 rpm are an extra unnecessary hazard to personnel and equipment,
and jaw slop is inevitably going to be greater and even if it weren't, the higher jaws will exaggerate the effect if you are trying to grab short work.
as to max. rpms, 15k sounds fast for a 16" independent cast iron body. a chuck's max depends on a number of factors, including if its a steel body or cast iron, and quality of construction and of the casting, if its a scroll or independent.
a scroll chuck can spin a little faster all other things being equal, as the steel scroll is pulling the jaws together, an independent jaw is relying on the body alone to push the jaws inward, adding to the forces pushing outward.
having said that, unlike what some others have said, I highly favor having one that maxes out your lathe, or nearly so, as an option.
not all work will be over the saddle, and not all work will send the jaws past the body. for example, I have a small drill press table mounted on my Graziano SAG 17 right now in a 15" 4 jaw chuck, and it's obvious lots of work can be gripped with the jaws in the O.D. config. and be a facing job.
you said you started as a wood shop. don't know if you ever make bowls, but that's another use for the swing you have.
the 12" adjust true is a decent primary chuck for this lathe, and even if you had a smaller lathe, I think a 6 or 8 would be good to have as well. you may have the smaller lathe set up for collets and want to do a smaller job. in fact I might not bother making a backplate for the 5C chuck for this lathe (I think you said you were intending on doing that?) if you get a Hardinge or other smaller unit that is optimum for collet work.
you will most definitely want to rig something to assist in changing chucks on this baby!
good luck and happy turning!