14 gauge will handle 15 amps.
12 gauge will handle 20 amps.
Google "ampacity of copper wire" Even though my spell check says that "ampacity" is not a word, trust me, it is.
The cheapest way to get stranded 14 gauge is to buy the cheapest construction-site extension cords at Home Depot.
Avoid anything that says it's for fancy home speaker systems. You're paying for hype.