John has accumulated $$8,000$ in credit card debt with an annual interest rate of $20\%.$ He is contemplating taking out a debt consolidation loan with a lower interest rate of $15\%$ per annum to pay off his credit card balance. The debt consolidation loan has a term of $4$ years.

a$)$ Calculate the total interest John would pay on the credit card debt if he continues making minimum payments without borrowing.

b$)$ Determine the total interest paid on the debt consolidation loan if John decides to borrow and use it to pay off his credit card debt.

c$)$ Considering the results from parts $($a$)$ and $($b$),$ provide John with advice on whether it is financially sensible for him to take out the debt consolidation loan to settle his credit card debt.