I’ve played with both the nGraver handpiece and the Foredom
PowerGraver set up.
They both worked quite well, surprisingly well really. Seems like I
found the nGraver a little more adjustable, and despite its blocky
shape, it felt more natural in my hand. I used both of them with a
dial speed control. I don’t know how well they’d handle with a foot
pedal, as I recall you’re supposed to keep the rpms fairly low. Cut
copper and aluminum easily, mild steel with a little effort. I’m sure
it would have cut silver too, since that usually cuts a little
smoother than copper.
I don’t know how you’d get a #15 to hold a graver, but I guess it
might be possible. I’m not sure the stroke length is long enough, but
I can’t say I ever tried.
Before you investigate some fancy collet system though, I’d just
grind and sharpen a graver point into one of the replaceable tips.
That way you could try it out before spending any money, less the
cost of a replacement tip.