Just to extend your example, that programmer would be a 10x programmer if the achieved goal (runs 15x faster and uses less memory) is valuable to the company.

Just to extend your example, that programmer would be a 10x programmer if the achieved goal (runs 15x faster and uses less memory) is valuable to the company. Adding value depends on the context. If the main problem for the company is that the feature set is not attractive to clients, then speeding things up 15x and using less memory may not make a difference. If however, the feature set is amazing, but customers complain about the product being slow and eating up too much memory, then said programmer is adding a lot of value, thus "becoming" a 10x programmer.