No need to mention 2016 & 2015. I did the same way and got AOR.My wife recently applied for citizenship. There was a question whether she filed taxes in the last 5 years. She did for 2017, 2018 and 2019 and she marked as yes for both required to file and taxes filed. This was done with help from CRA. However did she also have to mention 2016 and 2015. She immigrated to Canada in August of 2017. Was never in Canada before that. So she only mentioned those 3 years.