Besides RAM, Bluestacks also requires a good CPU to process the information. However, you can adjust the RAM allocation for the application using the registry.
Go to Start > Run > regedit and navigate to the following location
HKEY_LOCAL_MACHINE\SOFTWARE\BlueStacks\Guests\Android. Double click the memory and then select the Decimal option. Assign 1024 or higher (2014 but no higher) and then reboot the PC. It should work OK now.