My OS (Windows 10 Pro), and the game, is on a M.2 NVMe. It's not a hardware issue. I have 146 porn games (so far) from F95 (made using Renpy, Unity, Unreal, RPGM, HTML, you name it) and this is the only one that loads and transitions slow.
When using the HTML you get "Now loading", so at least you know the game is doing something. But when running the exe, on a transition to a new scene the game window goes completely black (the UI vanishes) and stays that way for many seconds (now close to a minute) before something finally gets displayed again. First time this happened I thought the game had locked up. But, no, it just goes out to lunch (a completely blank black window, no icons or text, nothing) for an extended period, with no indication that it's doing anything, until eventually it deigns to display the next scene and the UI gets restored. That's a coding/engine issue. I don't think that any of the other games that I play use the engine that this game is using, so I can't compare and say for certain whether it's the coding or inherent with the engine or a combination of both.