1. Select the first image from the default background images of incoming calls.
2. Optimize your phone by using Optimization app .
3. Secure memory of your phone by deleting apps not in use .
4. Uncheck Couchgram from power-saving app list in power management app.
5. Spam-filtering app or caller-ID app may also cause the delay of the incoming call screen.
6. Game or other heavy apps may cause the delay of the incoming call screen.