Oven cooking queue problem: need help to determine its nature
This problem is NP-hard: it is a more general version of Minimum Multiprocessor Scheduling. You should not expect efficient algorithms that compute the optimal solution in all cases. 

The main difficulty is finding out what is the "best" oven in which to cook an ingredient. Once you know (in some way or the other) which ingredients should go in which oven, you can not go wrong by queueing them based on their preparation time.  

So one way to compute the best solution is as follows: perform a cycle in which you try all possible assignments of $K$ ingredients to $N$ ovens, which is $N^K$ possibilities. For each of these possibilities, compute the solution based on queueing by preparation time in each oven. The best of all solutions you generate is the optimal solution. This of course will only be practical if $N$ is very small (like in your example) and $K$ is also small.