The Universal40 is a complete replacement for an older Hayward/Goldline system of any size. It will be a direct fit for you plumbing and uses the same type of electrical, so it should be very easy to switch. If you are asking if you can use the old T-Cell-15 on the new Universal40 controller, it will not work. The Universal40 uses a cell that is much more powerful, and the T15 cell would likely give you incorrect salt readings and cause a warning light to come on.