What will be the output voltage if I supply 1.5V to a 3V to 32V XL6009E1 voltage booster?
The datasheet for the XL6009E1 says it operates on 5V to 32V.

1.5V is outside of its operating range.  You can't count on it doing anything useful on that voltage.

If you try it and it works, then you still shouldn't do it.  There is no guarantee that an IC from a different batch will be as tolerant of the low voltage.



You would do better to find an IC designed for the voltage you need.

Something like the LM2621 from Texas Instruments or any of the many boost regulators you can find if you search for 1.5V to 12V boost converters.