Welcome to the board.


If you want to permanently increase the numbers by 15% then:

• Type 0.15 into a spare, empty cell. Let's suppose this cell is cell Z1.
• Select Z1 and press CTRL+C to copy it.
• Select the cells containing the numbers which you want to increase.
• Right click > paste special
• In the Paste section choose Values. In the Operation section choose Multiply.
• Click OK
• All of the numbers will now be increased by 15%

If you want a formula to reference a given cell and provide a result which is 15% more then this will be the general outline:
=A1*15%