Yes, the SV has more deep bass than the Fifteen, but that’s to be expected. The high switch on the SV allows for more clickiness of finger/pick attack of the string to come through, even with the treble knob rolled off. Obviously having the mid control on the SV gives you options that aren’t available on the Fifteen.
Mine are hooked up in series but I’m not running one into the cab sim of the other, if that’s what you mean.