@Mattk I don’t know what you mean by “dilutes” the latest queries. If a topic is actively being discussed or worked on, it deserves to float to the top. If a “new” topic gets solved quickly, it should sink to the bottom to make room for others. This is how almost all online forums work, and is a paradigm that has evolved over decades, and one with which most participants expect them to function.
As others have suggested, even if the mods decide to keep this auto-close after 15 days, I see no downside in allowing the topic re-open if new information comes to light (up to a reasonable amount of time—I support permanenty closing topics after e.g. 6 months or 1 year to discourage necroposting).
Real World Examples
I started the topic Upgrading to Tailscale 1.70 breaks web interface on 7.08 which, as of today, is still an open unresolved issue. Yet, because of the arbitrary topic closure time, the topic has been closed. Now, if or when a fix is released, I will not be able to post to the original topic. I will need to start a NEW topic, and then paste a link to the closed topic which is not efficient and makes searching more difficult for others.
This happens OFTEN. Here are a few other examples of topics that got closed with no answer or resolution: