Ok, so guyz today I called the Institute and asked questions about the scholarship waiting list. They told me that we might hear about waiting list decisions throughout the next week or two weeks. They also said, that it is theoretically possible not to have any answer by April 15th. If so, she told me to call them on April 14th and they will let us know the decision before the payment deadline.
As it turned out they have ranking within the waiting list. The lady told me my chances depend on which number I have within the list. She said they are busy sending admissions now and can not look up my number, but if I call her next week, then they might tell me my number within the list.