Hi,
You have "product 1" and "product 2" in your cart.
"product 1" have a shipping price for itself set to 8 and "product 2" have a shipping price for itself set to 7.
The logical final shipping price is :
[global shipping price in the config] + ( [price per product] * [products] ).
And the shipping price per product can be overridden for each product.
Your shipping configuration set the "shipping price" to 0€ and the shipping per product default price to "empty".
So the shipping total is :
0 + (7 * 1) + (8 * 1) = 15
That is perfectly logical with the feature which is called "shipping price per product".
Now if you want a totally other feature which use the higher price of a field of the products in the cart, the best will be to implement a special shipping plugin.
Using a "product custom field" you will be able to let the admin choose the special shipping price for each product and your special shipping plugin will read the cart content to determine the maximum value ; which will become the price of the shipping method.
But the feature of the "shipping price per product" does not work in the way you want.
Regards,