You say your mortgage rate is 1.5% for the next five years. In the current climate that's incredibly low. There are some savings accounts that pay higher interest rates than that. You are likely to be able to find safe and secure investments that will pay better than that. If that's the case then you should not pay off your mortgage, but instead invest the money.
Investing in the stock market is risky. You might make a ton of money, but you might lose some as well. If you are OK with the idea of perhaps losing money then go ahead. But if you are not there are plenty of alternatives.
The safest are Fixed Income investments, where you give a bank your money and they pay you a fixed interest rate and then give you back the money at the end. The interest rates are usually higher than a savings accounts, but not by much.
The next best is what we in Canada call a Mutual Fund, and I believe is called a SICAV in the Netherlands. They come with various degrees of risk, and if you pick a conservative one you are very unlikely to lose money. Average rates of return are significantly better than Fixed Income.
However the best advice is to consult an investment professional about where you might put your money. They can advise on likely rates of return and degrees of risk. They can also advise about tax implications. These are important to your decision because you will pay tax on any investments you make, but paying off your mortgage is essentially "tax free" - you don't get taxed on mortgage payments you are not making.
The other thing to think about is what else you might need the money for. If you might have a big expense coming up (getting married, getting more education, buying a yacht) then keep some money where you can withdraw it at the right time. Also make sure you've got a little bit money easily accessible in case of an unexpected expense.
In my unprofessional opinion you are going to easily be able to find a safe, secure investment that returns better than 1.5%, and so you probably should not pay off your mortgage.