I'd get a multi-sized tool for ease/future compatibility, but 3.3 is the "standard" (I think).
15 on a multi spoke tool will depend on the manufacturer, often they just produce a tool with 0.5mm increments and could start/finish wherever they like (again, I think).
0.127" (3.23 mm) (DT/Wheelsmith nipples)
0.130" (3.30 mm) (most European)
0.136" (3.45 mm) (most Asian)
I'd get a multi-sized tool for ease/future compatibility, but 3.3 is the "standard" (I think).
15 on a multi spoke tool will depend on the manufacturer, often they just produce a tool with 0.5mm increments and could start/finish wherever they like (again, I think).