Trouble combining two formulas and retaining both outputs.

Hi all,
I am struggling to combine two formulas which are essentially two halves of the same end result into one formula.
In one cell, I can get the formula to return a value if an amount is required, and in the other cell, I can get the formula to return a comment "Not Enough" if there is no amount or not enough available.
However, I cannot seem to combine both sets together to give me one formula.
I have attached a sample file and highlighted the cells in yellow.
M15 works as it should, O15 works as it should, but N15 is where I have tried to combine them and it's returning a value error.
Can anyone help on this please?

Thanks in advance.