I don't have the ruffler for the 15000, but I do have lots of vintage binders and some of the later ones are exactly the same - though unfortunately the ones I have are for low shank machines.
The ones I have work well on the machines I've tried them, but to be honest I don't do much ruffling/gathering and I have probably done more gathering with just a gathering foot. Not sure if there is one for the 15000 but there probably is.
I've thinking of looking for a vintage high shank ruffler to try (as the Janome one is way too expensive), or I guess I could try using a low shank one with the high to low shank Brother adaptor I bought so I could use my low shank screw on feet (haven't really tried that with anything - there are 2 of them so not sure I got the right one, so may have to get the other one as well to compare - no one I asked seem to be able to tell me the difference and just kept asking me which Brother machine I wanted it to fit and I don't have a Brother machine!)
"Live like someone left the gate open". Kimberly Burnham