15M length should be an Edge FX refill only. Are 45M Edge cartridges available? You could convert an Edge cartridge to Edge FX with a kit made by Gerber or Graphic Marking Systems. I believe the kits are ~$40-50 USD and they are reusable. (or using a table vice, hacksaw, and plasti-weld you could try making your own using a set of caps for each system)