Pension fund: 3% guaranteed over CPI or split 50/50 with SP500 over the next 15 years?

Dear all, I would like to pick up your collective financial brain. I work for a UN agency and for our pension we have different investment options (this is not a 401K). We can contribute up to 11% of our gross salary and the employer matches it 100%. We can compose our portfolio as we want selecting 20% of this, 10% of that, etc. I am pretty sure we have a "special" option which is the "3% option" which guarantees us 3% net over the CPI of the month of April (example for this year - Real 3% Annual Percentage: = 3% + (CPI 4.98%) = 7.98% guaranteed for this year). Out of this we have S&P500, Russell 2000, and others (see link). Should I split 50/50 the investment option with the S&P500 index or the 3% option is unbeatable? I have been with this agency since 2016 and missed the bull run in the S&P500 of the last years. My time horizon is the next 15 years. Wanting to add some diversification/boost to this option is a fool's errand or make sense? I believe 100% investment into the 3% option guarantees returns during tough times but when the tide turns I could miss significant gains. Should I wait to see what happens in 2024? Grateful for any of your insights.

Investment choices returns

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