I noticed switching to a "big" channel had a big delay, 22-37 seconds before the channel panel would come into focus.

TIL that this was primarily caused by having view join/leave entries enabled.
TIL also that timestamp and the join/leave information is logged into scrollback history even if not selected.
TIL that the channel options for timestamps and join/leave toggle viewing of these on and off. The entries are kept in the scrollback history regardless of whether viewing that information is selected or not.

When I clicked to switch focus to channel Testing, which I was already joined to, it took 37 seconds for the channel to come into view. Then I turned join/leave off. After swtiching to another channel then switching back, it only too 2 seconds for that channel to come into view. I turned join/leave on again, and the delay to view was again 37 seconds.

My takeaway is to keep the join/leave view off.

If I want to see some history of that, it is there. I can enable the view, wait xx seconds then see when so-and-so joined or left. But keeping that view function disabled makes switching between channels MUCH faster.

That's funny cuz it'd mean the chat would freeze regardless later on once there's a lot of chatting going on. Unless there's a setting to limit chat history like with logs.
One would think the operating system had become smart enough to not freak out about long text views... sadly it's not. You can observe the same stuttering when browsing long shares in Tixati. I think some apps try to fix it themselves like Notepad++ but damn is that a lot of unnecessary work.

This has been fixed in version 1.16.

We had to re-write some of the rendering code for Windows platforms.  There is now a nice new layout engine that uses Uniscribe for low-level glyph rendering, and it's much faster.  Flipping between channels shouldn't take more than a second for a very full buffer.