Nothing wrong with 15.75mm for the Corris - see our about page which states:
This typically, but not exclusively, means using finescale or exact prototype standards and correct gauge. Those modelling nominal 2ft railways in 7mm scale use 14mm gauge track (hence O14), 17.5mm for 2ft 6ins, 21mm for 3ft, etc. (and often Scale7 for standard gauge).
