Mortgage at 2.65% vs investing: pay down or invest €25,000?

Hi everyone,

I’d like some input on a financial decision I’m considering.

Mortgage details:

• Remaining balance: €151,126.64
• Remaining term: 277 months (~23 years)
• Interest rate: 2.65% fixed
• Monthly payment: €729.94

Available cash: €25,000

I’m considering three options:

1. Mortgage prepayment reducing the monthly payment
2. Mortgage prepayment reducing the remaining term
3. Investing the €25,000 long-term (index funds / ETFs / stocks) over ~23 years

I already invest in an S&P 500 ETF, and I believe adding MSCI World would be somewhat redundant due to heavy US exposure (please correct me if I’m wrong).

👉 Main questions:

• Does it make sense to prepay a mortgage at a relatively low interest rate like 2.65%?
• If investing instead, which assets would best complement an S&P 500 position?
• Would you split the €25,000 between mortgage prepayment and investing? If so, how?

Profile: long-term horizon, medium–high risk tolerance, no short-term liquidity needs.

Thanks in advance!