I am a bit late to this thread but.
Yes, code may say that a branch circuit is breakered at 15 amps and the plug itself can handle 15 amps, but in real life, they will NOT HOLD UP to hours upon hours of this current. You WILL burn up the plugs! BOTH SIDES of it.
They get hot, which at first may not be that big of a deal, it's just 'warm' but over time the female spreads, gets looser, now it gets very hot up in there, and then that makes the problem worse, now stuff starts melting / burning up.
Charging your car / bike is going to take HOURS ! You might get 6 months out of this cord before it's wrecked. BTW as it burns itself out if it starts arcing / snapping, that little ripple or noise, whatever you want to call it, the harmonics of that tends to be real shitty on hi freq switching power supplies / chargers, especially any electrolytic caps in there, you will bulge them.
IF you must run 14 gauge, id recommend 10 amps MAX. If you are running 12 Ga, id recommend 12 amps before it starts getting too hot after time. This is of course if you are running a 25 or less foot cord. If you are running 100 feet of cable, the line drop is going to get you as well..
Aaron