current loop transmitter with higher regulated voltage
If you are asking if you can run the XTR115 from your +12 volt supply the answer is yes since it will work with 7.5 volts up to 24 volts (recommended maximum).

If you are asking can you generate a 12 volt supply from the internal 5 volt regulator of the XTR115, that would not be the best choice due to current limitations. You would be better to add a buck/boost regulator off of whatever is the voltage supply to the XTR115.