I am having difficulty with the cell reference function. Is there any way to maintain the result from a referenced data without keeping the referenced cell?

To clarify, suppose I have a cell (A15 for example) and it contains data (18, for example). I have another cell (B15, for example) that contains the following formula =A15+3. The result in cell B15 shows 21. Is there a way that I can make it so that this data becomes absolute and cell B15 will remain 21 even if I delete cell A15?

Any help would be greatly appreciated...