Is it permissible to buy a car at a reduced price through financing (€13,500 instead of €15,000 cash)?

There is no objection to the price of a car differing between cash and installment payments, as long as the contract is concluded on a fixed price. As for financing, if it is a loan with an increase, then it is forbidden usury (riba). However, if it is a correct murabaha (where the bank buys the car and takes possession of it, then sells it to you in installments without a late payment penalty), then it is permissible.