The Startup Time to the Main Menu is the culprit It's most probably because they load at least 1 entire map before as the Main Menu Randomly displays a entire Map (Room) as the background that also sometimes doesn't get used yet but will be coming as seen on their Patreon as a harem and most probably gallery location as well

Im not sure if they actually preload more i didn't take it apart so deep yet but of course the pre map loading takes a bit more time and i hope it's not only done to look cool for the Main Menu but to be actually faster from Main Menu to Map which makes sense though it's often the other way first you get as fast as possible to the Main Menu then you take your time Loading (Streaming) the Level Data without Pre Loading it right from the execution.
Im doing my loading Streaming Multithread efficiency tests over USB3 it takes some time
SATA HDD USB3
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Start (Planet Picture)->Main Menu = 0:52 sec
Main Menu-> Gallery Start = 0:52 sec
SATA SSD
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Start (Planet Picture)->Main Menu = 0:18 sec
Main Menu-> Gallery Start = 0:18 sec
Tough im doing Hardcore at the Edge of System Resource Efficiency testing
So HDD total 1:44 min (Scene Pose Setups then load fast)
SSD Total 0:36 sec