Sorry, but that does not work for me.
I try to explain it differently.
Customers can buy free from a value of $ 30.
The exception is the special product for $ 15. Here the buyer must buy at least 4 pieces, so that these are free shipping.
But there is a special feature: If the customer buys from the special product only 1 piece and additionally for another $ 30 other products, so a total of $ 45, then the order is also free shipping.
There would have to be a possibility to check if the special product is in the shopping cart, the quantity is 1, and other products in the shopping cart totaling $ 30 ($ 45 together with the special product).