A 15 mm stone at the Pelvi-Ureteric Junction (PUJ) is relatively large, and after ESWL (shock wave treatment), it is common to feel pain as the stone breaks into smaller pieces and starts moving down the ureter. This movement can cause sharp or cramp-like pain, sometimes quite severe, especially in the first few days after the procedure. Pain relief medicines and medicines to help the stone fragments pass are usually given, but they should be taken only as advised by your doctor. If the pain is very intense or not controlled, your doctor may need to adjust the treatment or check whether a fragment is stuck. You can help reduce discomfort by drinking plenty of water to flush out the fragments, unless your doctor has advised otherwise. Applying a warm compress to the painful area and taking adequate rest may also help. Try to stay active with light movement, as it can help with stone passage. If you notice fever, vomiting, difficulty passing urine, or unbearable pain, seek medical care immediately, as this may need urgent attention.