I'd expect that a shop that spends upwards of $2k on a tool would know how to use it. However it's possible you ran into an employee who was more interested in trying to please, than knowing the limits of his knowledge. This is fairly common, years ago most shops had to keep the various cutting tools used in frame prep under lock and key.

Anyway 15g spokes are fairly rare, and I wouldn't be surprised if half the shop rats wouldn't notice if you didn't mention it. As for the length issue, the length stop on the Phil needs a bit of touch to produce consistent sizes.

I own a Phil machine (early serial#) and yet prefer to stock the 10% of sizes that I use 90% of the time. The Phil machine is for the 90% of the sizes that I only use 10% of the time. There's little or no discount for blank spokes vs cut and threaded ones, so hand threading all spokes is simply an unnecessary expense in time.