Quaternium 15 is a preservative. It is placed in a number of skin care products, shampoos, washes etc. It helps especially to prevent infection from the Pseudomonas bacteria. It is the most common preservative-based trigger of an allergic cotact dermatitis. So you are not alone.
Quaternium 15 releases formaldehyde. So many people who are allergic to formaldehyde will break out to this ingredient too.
You will have to become a label reader. The FDA requires that ingredients must be listed on the box the product comes in. It would be impossible to name all the products that do not use this preservative. Just learn to avoid it.