Disable all blackground apps when using some apps (possibly with Tasker)
You can do so by forcing the system to limite background processes. Open the Settings > Developers Options > Limite background processes and select No background process. 

If Developers Options is not enabled (on Android 4.4.2 and above), enable it at Settings > About phone > Tape 7 times on Build number > Go back to Settings, the option should be on.