You don't say what language this is, so I will assume it is python. But in every programming language I have ever used, decimal places are separated with a "." and not a ",".
When calculating the voltage of a signal connected to the analog pin of many types of Arduino, it is necessary to divide by 1023 and then multiply by the voltage at Vcc (normally 5V but 3.3V for some Arduino models). This is because the ADC on many types of Arduino is "ratiometric" by default, meaning an ADC value of zero means 0V and 1023 means 5V (or 3.3V). The 1023 value is because most Arduino ADC have 10-bit resolution.
However, the ADC in ADS1115 is not ratiometric, it returns a value which corresponds to an absolute voltage. So there's no need to divide by 1023.
However, you may still need to apply a factor to the raw value from the ADS1115 to turn it into an absolute voltage. This depends on the library (either C++ or python) you are using, which you don't give any details about.
I don't think using your Nano in place of the ADS1115 is a good idea. It only makes things more complicated, plus the Nano's ADC is less accurate than the ADS1115.