Upgrading to an SSD for a speed boost?

Hi there!
I have a quick question regarding how I should manage my storage space between an SSD and a traditional drive.
A little context: I ended up picking up a MacBook specifically because it’s the only machine that runs Program X properly.

Mostly, my setup consists of a 24GB SSD paired with a 1TB Hard Disk Drive.
Right now, both the OS and Program X—which is my main priority—are sitting on the Hard Disk Drive, leaving the SSD completely empty.

The operating system takes up about 10 GB, while Program X needs roughly 20 GB.

So, here is my dilemma:
If I want to optimize the actual performance of Program X while I'm working in it, would it be smarter to move the OS to the SSD, or just install Program X there? I can't fit both on the small drive.
As it stands, my boot times are sluggish and apps take forever to launch. I suppose I can live with that, though—my real goal is to speed up the responsiveness of Program X during active use; I don't really care much about loading speeds.

To recap, if the goal is maximizing the runtime efficiency of Program X, should I prioritize the OS or the program itself on the SSD?

Thanks 👍

Obviously, you gotta run the OS on an SSD. I don't see any point in having one if it's just sitting there acting as a secondary storage drive for files.