The original game uses hardware rendering but needs 1 GiB or so VRAM. That's the reason Daytona675x gave for switching to software rendering.
Okay, but then why port such a hungry and obviously bad programmed game in the first place?
On a PC you may waste resources like this, but if you plan to release it on different platforms, you have to take some special care, especially if those target-platforms are magnitudes weaker as the original HW. You need a different rendering-path with some kind of texture-streaming, even if that means you have to pause the game at some door and load the next sections, like in Half Life 2. In such a game, the scrolling must be absolutely liquid and unnoticeable.
I don't blame Daytona675x, maybe he did the best possible to bring this mess in shape. I blame the concept of advertising and selling a game for "Amiga NG" which then does barely work on the fastest machines available. If it can't be done properly, don't do it.