I am making my application accessibility compliant. for this providing correct data to the accessibility framework by giving android:contentDescription="your string" in xml.
Also I have Seen the Android Developer guide on Making Applications Accessible for an overview of what steps you need to take to ensure your application works correctly with accessibility services.
Now problem is testing these all in each and every screen taking more time. my app has 30 screens and each time to go to any module will take almost 15-20 mins when talk back is on.
can anyone suggest tool/ better way to test app?
@unof is right, one tool you can use is lint to show you some warnings for missing content description.
I'm also experimenting with the Google Accessibility Test framework, it can help you to automate some of your tests: https://github.com/google/Accessibility-Test-Framework-for-Android
Besides that also a good advice is to use an emulator that supports talk back, I'm using Genymotion with Gapps installed and is much easier/faster for some cases than using the actual device, if you are going to test multiple gestures, I'll recommend using Genymotion remote control feature: https://docs.genymotion.com/Content/03_Virtual_Devices/Emulating_sensors_and_features/Remote_control.htm it's very handy in situations when you need to track your network request while using the two fingers for scroll as accessibility requires.
Still is a manual task you will have to do, so try to tweak it.
Go to the Accessibility settings and increase the speed at which the text is spoken: http://developer.android.com/design/patterns/accessibility.html#tools
It's also helpful to learn some of the gestures, and to explore the TalkBack settings: https://support.google.com/accessibility/android/answer/6006589?hl=en
I hope it helps!