High sierra has created some problems which I have read have been fixed by the latest preview build of 2017.
Assuming you purchased 2015 direct and not through Apple you are entitled to a free upgrade to 2017. If your purchase was for an earlier version the you can get a 50% discount and obtain a new key by entering your existing key into “Upgrading?” box at https://infinitekind.com/purchase
So, download and install from https://infinitekind.com/preview
Then enter your existing or new key as appropriate.
Just install it over your existing build.