I haven't. Even though the earbuds don't support 15W charging using a 15W charger shouldn't damage them, as they won't draw more power then they support. Same way if you used a 45W charger on your phone, but your phone only supported up to 25W charging it would only draw up to 25W. I've even used a 20W Charger on my buds live and it's never damaged them
They support fast charging. On Samsungs website they say "Five minutes gets you an hour" and mine charge just as fast in the case. They also aren't huge batteries to begin with (in the earbuds) so they can charge pretty fast, but still last a long time
