My calculator says 0.69 psi for 1.5 vols at 38 fahrenheit.
Have to say that it should be served at around 54 fahrenheit and if carbing at that temp for 1.5 vols its 6.25 psi.
If you were going to carb cold and then warm up remember to adjust your regulator when you get it warmer.
Big but here very low readings and adjustments on a regulator are difficult and you might need to use an inline regulator on a different scale or check very closely with a separate gauge to cross check your regulator reading.
I use this calculator
Beer Carbonation Calculator
Note if you went to 1.2 vols which wouldn't be unreasonable either you'd be overcarbed at 38 F.
Further some places serve this on draught with nitro so you could try a stout tap and see what difference it made to your beer.