There is no absolute answer here, as your ability to understand a spoken language will depend on many factors beyond the realities of its written form. However, an interesting case study on this point is the Peterborough Chronicle, which, written in the second quarter of the twelfth century, represents an intermediary step between Old and Middle English. There is a section here with an audio recording, so you can see how you do understanding that. (If you look around that site there are other middle english texts with recordings you can compare it to.)
Hi there! There is always room for more discussion, but this question gets asked here fairly frequently. You may be interested in this section of our FAQ:
If you want to follow up with anyone who posted in those threads, mention them by username here and they should get a message. Thanks!