Is a KNN-Classifier memory intensive?
KNN is a memory intensive algorithm and it is already classified as instance-based or memory-based algorithm. The reason behind this is KNN is a lazy classifier which memorizes all the training set O(n) without learning time (running time is constant O(1)). 

Inversely, When it comes to querying new points to find the nearest K, the query time will be  expensive O(n) in terms of the running time.