Question about ADS1115 resolution and v_ref

I am trying to understand ADS1115 code. Because I want to get third battery log to using ADS1115.

But, I wonder why rosolution looks like 15 bits.

16 bits → 65536

But, In the code, the resolution is 32768.

_adc_report.resolution = 32768;
_adc_report.v_ref = 6.144f;

I don’t know why v_ref is 6.144.

And… I want to log third battery log.
Is it possible?

battery_status_2 ← I want

I found the reason why 32768. One bit was used as sign bit(+, -).
But still i have question about third battery log.