Creating a multisite while having a WordPress site running in subfolder

Hi!

I’m working for a yearly event organization and the staff asked me to make a website with different subdomains. I’m going to work on the second year so I have to put the last year’s website in a third level domain such as “2015.bitumephotofest.it”, and make a new one such as “2016.bitumephotofest.it” for the upcoming edition.

The current website is in a subfolder.

I’m considering to create a multisite network but it is difficult to me to understand if it is convenient or not. Maybe there are easier way to achieve what I need.

Should I install a multisite network in root and then “link” it to the subfolder that I have?
Should I turn my subfolder in a multisite? How to make the upcoming edition subfolder then?

I’m a bit confused.
Does anyone know how should I do?

Thank you in advance!