Since support ended in April 2019, I decided to finally do the upgrade to version 18. My main reason for not doing earlier was general laziness, and a worry my encrypted system might not make the upgrade safely. Backed everything up first for safety. The mintupgrade program took 70 minutes to complete, needed some Y/N questions answered, but when all was finished, it worked OK. So, anyone facing the same upgrade, go ahead, it works for encrypted system too.