In the Owned Games list, I had it set to group by Installed. As of 2.0.14 and still 2.0.15, it no longer remembers this and reverts to not grouping when I restart the client. It still remembers other customization settings like sorting, visible columns, and grid/list view.

That's been consistent in all versions of 2.0 I've seen, and is one of the points I noted here:
https://www.gog.com/forum/general_beta_gog_galaxy_2.0/open_letter_to_gog_and_message_to_support

That's strange. It only started happening to me with 2.0.14. I've been using it since the early closed beta, and it would remember my custom view settings between session.

I wasn't in closed beta, and haven't paid close attention to version numbers, so all I can say is that all the versions I've seen have done it. Not specifics of which versions that was.

I have reverted (as I noted in that topic) because of concerns about losing the ability to actually use the client to install and launch my games, something which I've seen a number of users report as a problem with Galaxy 2.0 and which hasn't happened to my knowledge with older builds.

I will add a me too for this.

There was no issue in 2.0.14, but in 2.0.15 the 'group by' setting under 'Owned games' is not remembered between restarts of the GOG Galaxy client.

There is a workaround for now. Go to Settings \ General and set "Starting page" to "Continue previous session".

I confirm this works for me.

Thanks Hustlefan.

You're welcome. :)