No, goldfish are very hardy fish, but they won't survive for long in the set-up you're describing.
You need a much larger tank for the fish, because goldfish produce A LOT of waste in the form of ammonia, and ammonia is toxic to fish. Its good that you're doing plenty of water changes to help dilute that waste, but that causes two other problems: large water changes are physically stressful for the fish, and you're removing the only place for the beneficial bacteria to live in your "aquarium."
I suggest buying a used 10 gallon tank (or 40L) tank as a minimum, and getting a filter that's rated for tanks twice that size. The beneficial bacteria will live in the filter and make the water much more hospitable for your fish. You should also get a water testing kit so that you can make sure the ammonia and nitrite levels are remaining at 0ppm. It'll still be necessary to do regular, probably weekly, water changes to remove the nitrate that will build up in the water and to vacuum out the fish poo and other gunk that settles at the bottom of the tank.
Ranchu goldfish are really beautiful, and if properly taken care of will live many years.