Difficult issue - especially as the BT14/15/16 frames were effectively identical. It's a 1965 Brabham and I suppose BT15 is closer than anything. So it's more a BT15/10 than a BT10/15, given that the frame and suspension are BT15-ish and only the body is BT10.
As the frame was at MRD and not at Arch, it's less likely to be a used frame.
To be frank, my system can't cope with this one
I think I prefer Brabham BT15/10 [AM24]-MAE
Allen