A 15 percent discount is a discount on merchandise or services that takes 15 percent off the purchase price.
A 15 percent discount is a good discount although 50 percent discount is much better.
If the original purchase price of something is $100.00 and you get a 15 percent discount then that item you purchase would only cost you $85.00
Since 15 percent of $100.00 is $15.00 that would mean you save $15.00 on that purchase price.
So every time you see or get a 15 percent discount you're saving a good percentage.
Discounts are always nice no matter what the discount.
The same goes for 15 percent off sales etc.
It means you're saving money on the purchase or service.