Your schematic already looks a little suspect with a 15V input and a 12V motor wired direct to that.
Note: On schematics, where something is an input or output and you don't have a connector plug to draw, always make a little line going off to "nowhere" and put the label on that line. You have labelled one node "15V" on a "net" of wires and there's no indication where this magical 15V arrives from.
Note2: Ground symbols. Use them.
So far it looks pretty good for isolating the Arduino from the raw 15V and brushless motor. You have an appropriate power supply chip with appropriate capacitors on both sides of it. Unelss your wiring is especially messy, this looks like it should work.
Since you have (hopefully) stable 5V, you should wire this directly to the Arduino's 5V pin. Going through Vcc pin means the Arduino gets less than 5V to work with.