Are you able to upgrade the phone to Android "Marshmallow"? If yes, then you could try making the card "Internal" rather than "External" storage, but to do so you would have to start with a blank card. So You would have to move the data to say a computer before trying this. Also, it will depend on if that particular device has been blocked by the manufacture from using this option. Sadly some do.
How to turn external SD card into internal storage on "Marshmallow".
NOTE: Please be sure you start with a blank SD card. It needs to be blank because when the card is converted to "Internal" storage, it will be formatted (wiped) and encoded (making the cards data only readable by that device).
1. Go to device “Settings”, then select “Storage”.
2. Select your "SD Card", then tap the “three-dot menu“ (top-right), now select “Settings” from in there.
3. Now select “Format as internal”, and then “Erase & Format”.
4. Your SD Card will now be formatted as internal storage.
5. Reboot your phone.
NOTE: If you don't reboot the phone, many things may not work correctly, so make sure you do.
That said... if you cannot upgrade to "Marshmallow", or the phone says it won't allow this even running "Marshmallow", then you will have to either remove some things you have on the phone itself to free up space.