very positive. Only if it were said in a sarcastic tone would it be negative. But the tutor goes on to say they are looking forward (this means excited) to reading it

no, it's definitely positive, more than just positive, it's a praise

It is positive. It is a compliment to you to say that it is "interesting." It is a bigger compliment to say it is "very interesting." The teacher is complimenting you on finding an original topic. It is clear that it is a compliment. One way we can tell is that the teacher adds a second compliment: "Looking forward to reading your essay." The teacher wants to read your essay. It is straightforward. it is not ironic. The teacher is simply saying what they mean. One way we know this is that it is good for an essay to be interesting and it is a natural word to use. It is true that compliments can be used ironically or sarcastically. It would be unprofessional for an online teacher to do this, though. It would be particularly unprofessional with an English learner, because people cannot sense sarcasm until they are very proficient in the language. And it would not fit the context. Now, suppose that in a live schoolroom, a 13-year-old student doesn't seem to be paying attention to the lesson. The teacher walks behind him and sees that he is playing a video game on his cell phone. The teacher might say, in a sarcastic way, "Hmmm. Very interesting. Give me your cell phone. After school, you get an hour of detention." "Very interesting" is sarcasm. It doesn't really mean what the words mean. The teacher isn't really interested. The teacher is surprised, or annoyed, or angry.

It's positive in this case. It could be negative in other cases, for example when you learn some news that makes you suspicious or that you do not approve of. Did you hear that the shop has gone bankrupt and the manager was seen leaving town driving a Ferarri? Very interesting!

I think that "very interesting" has a positive meaning. Your topic keeps your teacher's attention. He/she even says that he/she's looking forward to reading your essay. In any case, it's your choice. You chose this topic because you want to share your thoughts (maybe you have new ideas about something). I doubt that the teacher is planning to criticize you or anything like that. Don't worry. Good luck with your essay!