https://bugs.winehq.org/show_bug.cgi?id=48354
--- Comment #2 from François Gouget fgouget@codeweavers.com --- The TestBot downloads the latest Gecko and Mono installers and stores them in siblings of the Wine build tree [1]. This ensures they don't need to be redownloaded for each wineprefix creation. Is that what you had in mind for the "shared mono and gecko installations"?
Also the actual wineprefix creation times are more between 13 and 28 seconds. They can be seen in the log of the Reconfig tasks [2]. Outside QEmu things are faster.
[1] https://source.winehq.org/git/tools.git/blob/HEAD:/testbot/lib/Build/Utils.p... [2] https://testbot.winehq.org/JobDetails.pl?Key=62613&f101=log#k101