no you are not doing anything wrong.

you have a few things working against you,

you are only near 80 skill

you are running into just some bad random number generator spawn rate as far as finding colored wood.

15,000 logs is not very much really. A small sample size.

I know on my lumberjack I have harvested 300, 000 normal logs (because I have put them on commodity deeds of 60, 000 each) since the changes without a single log of the higher colors (Heartwood, Bloodwood, Frostwood) during that time I have gotten some oak, ash and yew. So it is out there, either just keep trying or find another player vendor with boards for sale?

I am also guessing that your character is human?

Personally I think they went overboard with these changes, it almost forces you to become a scripter. Not that I am advocating that you become a cheater. But these changes have discourage many players.