You’ll have to explain me how 15 decoys are enough to make you untraceable, there is still roughly a 1 in 16 chance that a transaction your output is the real spend in a transaction where it is included.
Imagine you are A, and B and C are two different third parties
If B -> A -> C, then all good
But if B -> A -> B, then there is a 1 in 16 chance (in the best scenario for you) that in B's eyes, you were the real spend. Add to that the fact that most people don’t churn and B doesn’t have many customers, and it becomes a lot more likely that you were the real spend (I'd bet my money on it).
CEX or not, you’re still traceable