An interaction occurs when the whole is different than the sum of its parts. You can have a positive interaction if the involved attribute levels have a synergy or a reinforcing effect. You can have a negative interaction if the two together aren't as good as you would expect from their separate utilities.
Here's an example of a negative interaction: I like scrambled eggs, maybe they have utility of +5 for me. And I like chocolate - maybe it has a utility of +8. But I would NOT like scrambled eggs with chocolate syrup that would have a utility of -22 for me. The difference between the total value of chocolate scrambled eggs and the sum of chocolate and scrambled eggs is the interaction, which is -22 - (5+8) = -35.
In your case the total value of A1L1 and L2L2 is 30 + 57 - 54 = 27, so it's not as extreme as the chocolate scrambled eggs example. Respondents still like A1L1 + A2L2, they just don't like them together as much as you might expect.