It really depends on what you are doing in the forms. You have to review each and every form to determine if the upgrade will work in a test environment. I have successfully upgraded many farms and written PowerShell scripts to crawl my farms looking for InfoPath forms in Form Libraries as well as List Edit and New item forms. We use the resulting list of forms to first, check to see if they are still in use, then later, for testing. Probably the biggest issue is when you migrate from Classic to Claims Authentication. This may break your InfoPath forms if your are getting the current user and then passing it outside the form.
You will need InfoPath 2013 to update any forms that you bring to SharePoint 2013/2016.
I just answered a similar question here.