Is there any change in Nelly's attitudes toward Heathcliff & Catherine in chapter 1–15?

Nelly's attitude toward Catherine does not really change in these chapters, or throughout the book as a whole, for that matter. While she pities Catherine's untimely death, she feels Catherine is unpleasantly willful and is the author of her own miseries. Nelly thinks Catherine's attitude toward Edgar, during both courtship and marriage, is thoughtless and considers her abandoning Heathcliff by marrying Edgar a betrayal of their childhood affections. Her attitude toward Heathcliff is more dynamic and complex, however.
Nelly's opinion of Heathcliff initially seems to be that she finds him greedy and cruel, though she does seem to pity his isolation. She says outright to Lockwood that Heathcliff is "Rough as a saw-edge, and hard as whinstone! The less you meddle with him the better!" Nelly has known Heathcliff from childhood and so has a special insight into how he became the way he is, though her opinion of him is still colored by her own moral views.
When Nelly starts telling the story in chapter 4, she says that when Mr. Earnshaw first brought Heathcliff to Wuthering Heights she initially despised him like everyone else, since he was a foundling of foreign heritage (the characters' descriptions of Heathcliff and his speaking in a foreign language when he first appears imply that he may be of Roma or African heritage). She leaves him on the stairs during his first night there, instead of taking him to sleep with the other children.
Her contempt for the child Heathcliff fades when he, Catherine, and Hindley fall ill and Nelly must nurse them. While Hindley and Catherine complain constantly, Heathcliff stays silent and endures his illness with patience, which endears him to Nelly, though she admits "hardness, not gentleness, made him give little trouble." His lack of complaining, even in the face of being bullied by Hindley, makes Nelly believe Heathcliff is not vengeful. His genuine mourning in the face of Mr. Earnshaw's death, and his talk of heaven with Catherine, gives Nelly a glimpse of the boy's softer side, which influences her attitude toward him as well.
In his teenage years, Nelly seems to think Heathcliff is ill-mannered but still capable of redemption. When he mourns Catherine's turning away from him to the better-bred Edgar Linton, Nelly tries to cheer Heathcliff up by making him presentable at a Christmas party and musing that he might have noble Indian or Chinese heritage. Her conduct is almost sisterly here, with her giving Heathcliff advice when he asks for it; however, after Heathcliff runs away and then returns years later, she takes a darker view of him.
Between chapter 10 and chapter 15, Nelly finds Heathcliff cruel and greedy in his plan to get control of the Heights by manipulating the drunken Hindley. When he starts pursuing Isabella Linton, Nelly finally turns away from Heathcliff, thinking him quite malicious indeed in his obsessive revenge. While she pities him for his loss of Catherine and his unfair treatment in his teen years, she is appalled by his conduct and views him as monstrous.