Your best bet is to try to clear the loan amount as quickly as possible. At a rough quess I would estimate that you are paying approx €270-€280 per month for the €13500 if it was borrowed over 5 years? That €270 repayment could reduce the mortgage approval amount by up to €60,000.
You could also refinance it with the credit union, and it probably wouldn't show up on your credit bureau.