Yes, you can pay in 2 installments, without having to pay any interest.
You need to tick the box with ´pago fraccionado´ on the last page of the declaration and pay 60% when you submit the return, and the remaining 40% before the 7th of November 2016.
To be safe, please submit before the deadline for ´direct debit / domiciliado´ payment has passed as late declarations will not be able to make use of the ´pago fraccionado´.
Hacienda also offers the option for delayed payment, but you must support your request by evidence why you are not able to meet the payment, and propose a payment plan yourself (declare that you will pay in one year, three years etc.). There is a charge though, currently at an interest rate of around 5%. Up to 6.000 euros you do not have give any guarantee, over that amount you do. You need to apply for this option at your local Tax Office, or you can do so online, through THIS LINK. You will need to have a digital certificate installed on your computer, or have a Cl@ve Pin. Info on both electronic ID options in the Library on our website.