The size wrench to remove it should be 15mm.
13mm
It seems to me I use a 15 mm wrench to remove the engine oil drain plug.
Use a proper size box-end wrench or socket to remove the oil drain plug
15mm
15mm.
14mm
11/16th
14mm
T40
15 mm
I can't remember exactly but its big (for a drain plug) somewhere around 17 or 19mm.