Drupal Commerce Multiple Prices
Luckily you have figured the harder part, counting the 14 products on user's cart. Second part is easily done, and it's called 'dynamic price calculation' or similar terms if you would like to find further information on google.


Create a rule
Event: Calculating the sell price of a product
Condition 0: (which is very important) Entity is of bundle or Entity has field or else you wont see the second price field added to the product type. It's rules assertion internal stuff and is needed, but somehow it's name is confusing.
Condition 1: If there are 14 or more products in cart
Action: Set the unit price to a specific amount
The value you pass to the action above is simply the price value in the second field!


This page could be useful, Sell Price Calculation / The life of a Price Calculation