There is a fair bit of agreement amongst scholars that the default articulation was 'detached' until sometime around the late 18th/ early 19th century. This is clouded by the reality that performers were expected to add legato slurs as expressive devices. (These slurs are sometimes indicated in the score.) The answer to your question, then, is not entirely clear. However, I think it is fair to say that in this movement, the eighth notes can be played detached, and the sixteenth notes can be more legato. (I am feeling too lazy to cite sources here, but can provide them if necessary.)
Of course, your teacher may have other reasons for asking you to play more legato...