iphone 15 not that responsive as IOS 18 after upgraded to ios 26.5.2

For you question,You can also try these steps:

1. Go to Settings‑Accessibility‑Touch, make sure Touch Accommodations is set to default, turn off Reduce Motion if enabled.

2. Reset all settings: Settings > General > Transfer or Reset iPhone > Reset > Reset All Settings. This will clear system cache without deleting your photos or apps.

3. Keep at least 15% free storage on your device. Low storage will significantly hurt system responsiveness.