Are you a locked device or updating from an older version?
To install this firmware, you will need a Mac or PC with the latest version of iTunes (or Finder on macOS Catalina and later). Download iOS 9.3.5 for iPad 2 model iPad2,2 (A1...
Disable Background App Refresh (Settings > General) to help the aging A5 processor keep up. Are you a locked device or updating from an older version