ASD is a hole in the wall that separates the right atrium
from the left atrium, which are the chambers of the heart receiving impure and pure blood respectively. Because of this hole, blood shunts from the left side to the right side and there is excess flow of blood to the lungs.
1.5 cm hole is a moderate sized ASD. Ideally, it should have been detected and closed in your childhood. However, in many such cases, a diagnosis is achieved at this age only because the ASD usually does not cause any symptoms till very very late.
Having detected this, it is probably better to close this hole if there is any evidence that the right atrium and right ventricle
are enlarging in size or if the pulmonary artery
pressure is increasing. A detailed echo of the heart will give you the answers.
There are two ways of closing the defect - by open surgery or by using a special device which can be done percutaneously (through the groin, without open surgery).