I think these are good changes. In a way, they might even be easier to handle (in my point of view, at least), since a player won't need to worry about a single, specific thread hitting 15. With an overall of 15 for two threads, it allows for a more relaxed drive, even if they're maintaining more than one thread at a time. I'm not sure, but I assume most players have more than one thread a month, so...
Plus, with the other option of two threads or logs with a single comment, it drives for the creation of more plots, more posts, making meeting ac standards easier and the development of cr hitting new levels, giving Ruby City a new push.

Overall, seems like a good change. It's still pretty relaxed, while also inspiring more player activity. Pretty good!