Very low historical life expectancies are driven by childhood illness and maternal mortality. If you made it to 15 your life expectancy might be somewhere in your late 50s.

There isn’t data for life expectancy at 15 before 1950 for India here (when it was 60) but you can see the it for Sweden back to 1751.

https://ourworldindata.org/grapher/life-expectancy-at-age-15...