Thanks for posting. This exact pivot shoe is no longer available, but our 15-177 is very similar and should be able to replace it. This shoe, like your old one, works with Series 152 Coil Balances. Given the age, I agree that replacing the whole coil balance setup is probably best.
For each replacement coil spring you have to choose a spring weight, which represents the weight the individual coil can support. I would get as accurate a measurement of the window sash's weight as possible. A bathroom scale should do the trick. We have to be within 1 pound of the true sash weight for replacement balances to work. If the sash does indeed weigh 15 pounds, you can use just a single coil on both sides of the window: the S152-8 8 pound spring. This will equal 16 pounds of support total, which is close enough to 15 pounds exactly--but if the sash weighs less than 15 pounds, that won't work, so please check as specified.
If your old coil housing is undamaged you can reuse it; otherwise, see the 15-143, 15-144 and 15-145. These newer style parts 'sandwich' around each coil. Let me know if you have further questions.
