We are currently profiling using Chrome's Lighthouse, which is Chrome's tool for measuring Google page experience.
In general, it seems like most XenForo / VaultWiki combination pages profile well using the desktop option (generally 97% or better).
However, when using the mobile option, it appears to simulate 3G speeds and lower-end phone processors. Unfortunately over the last 2 decades, web design moved away from keeping transfer sizes and web pages small with the rationale "everyone has broadband and faster computers now," and only recently started shifting back after realizing how much browsing had shifted to mobile and how slow that was.
You can make sure your XenForo / VaultWiki installation is as optimized for Lighthouse as it can by:
1. src/config.php NOT having
$config['development']['fullJs'] = true
2. NOT having your forum in debug / development mode
3. downloading VaultWiki NOT having "Uncompressed Javascript" checked
4. using Setup > Options > VaultWiki: Site config > Minify static Javascript and CSS files = checked
1 & 4 seemed to cut about 2 seconds from my times. Unfortunately on a dev board I didn't have the luxury of trying #2 and 3, but I suspect it will cut a bit more.
In VaultWiki 4.2, this will get cut by a bit too (~60KB over 2 requests) since YUI is removed. Note that Lighthouse currently presents a false-positive for the bundled YUI version (vulnerabilities in 3.5, but 3.18 is actually used).
Also:
1. avoid having overly busy/long wiki articles / posts / etc (break up extremely long content into separate posts / articles)
2. keep your number of articles / posts / etc shown per page low (20 or less for lists, 10 or less for full posts, 5 or less for full articles)
Since Lighthouse is Chrome's tool for measuring Google page experience, and there is already a task regarding addressing Lighthouse results, this task is closed as a duplicate. See:
https://www.vaultwiki.org/issues/6089/