the people would be speaking Middle English which would be your first barrier, there is quite a lot of word commonallity but the structure of sentences is different.
The great vowell shift in the 15-16th century would mean that you'd probably be untelligiable.
like the word bite started off sounding like beet, then bate and finally as we know it today bite.
forgive me but I think this is one of the few instances where wikipedia might be a good source to recommend, it has several sound files which show the changes in how words were pronounced. https://en.wikipedia.org/wiki/Great_Vowel_Shift
Not discouraging more in-depth discussion here - particularly on English in 1400 specifically - but FYI, this is one of the more common questions in this sub, so you'll find some previous posts on the topic in the FAQ