I haven’t tried sewing a hem with a wide double needle on my 15000, because I have a CoverPro 2000. It creates the same problem when I hem my t-shirts. To avoid this I have tried a number of things
1. a stabilizer called - Knit Stay Tape. It’s made my SewkeysE - I have it in Ivory, Black, White and there is a light beige as well. It comes in a few widths. I like 1/2” as I also use this in the shoulders of my t-shirts. It can also be used in the side seams if they tend to ripple or in a very unstable knit as some of the rayon ones. I also have it in 1” and 1 1/4”. I cut the 1” in half if I run out. It is “iron-on” but use a press cloth to attach it as it will do funny things if you don’t.
2. Floriani Wet N Gone Tacky Tape is one I used recently and it is wonderful BUT, you can’t stretch your fabric. Why I really like it is because you can just press it on with your fingers, turn up the hem and stitch away. I was very careful, as I once tried this quite a while ago and found that the machine pushed the fabric on top stretching it a little then I ended up at the end with “extra” fabric - just a pinch, but I wasn’t happy and had to “unseen” it and do it over. It washes out when you put the garment through the laundry - wear it first - no need to not get that FIRST wearing when it is spanking, brand new.
These would work with a sewing machine as well as a Cover Hem machine.
I was able to get the Floriani product from my local Janome (and many other brands) machine dealer and the Knit Stay Tape from my hour away Janome Dealer. These should be available to you from some close by.
Also you can take a tacky washable stabilizer and strip it to use as was suggested. This also works with a a fusible knit interfacing that is very thin - I think it might be referred to as fuse-knit - get a light weight as you don’t want it to show or be bulky. We like our tasks to be easy while we make our garments. We just need to do some prep work and that sometimes seems to be a time waster but believe me it is not.
Cheryl - Saskatoon