There are a number of things that can factor into applications on a mobile device running slow. The two main issues are high memory usage and poor internet connections.
High memory usage occurs when your device has many background processes running, making it difficult for the CPU to keep up. Try closing other applications that may be running and taking up resources. A fresh restart of the device can accomplish this as well.
When your device does not detect an internet connection, it will continuously search for available ones. This can cause your device to run slow, negatively impacting the applications you are attempting to run. This will persist until your phone can locate an internet connection.