Basically any S&P 500 index fund [1] averages over 8% return over the trailing 15 years, even inflation adjusted [2].

Using [3] October 2009 to present gives an annualized return of 13.763% and going back 20 years to include the great recession returns 12.06%.

Post-tax current-day value scenarios:

Starting in 2004 (20Y):

    $500.00/mo:   $418,349.29
  $2,500.00/mo: $2,091,746.42

Starting in 2009 (15Y):

    $500.00/mo:   $252,413.58
  $2,500.00/mo: $1,262,067.88

[1]: https://www.financecharts.com/etfs/SPY/performance/total-ret...

[2]: https://dqydj.com/sp-500-return-calculator/

[3]: https://dqydj.com/sp-500-periodic-reinvestment-calculator-di...

That's not guaranteed, and not how you save for a fixed goal.

I don't know of any lower-risk and higher-interest alternative to the 30-years-fixed that is currently offered to US consumers, and based of the above answer, neither do you.