Dark Frames for Long Exposure on a tracker?

Shoot (15 minutes) x (However many frames you want) → manually shoot one dark frame (15 minutes). You can take a manual dark frame by putting a lens cap on the lens before taking the shot. You're done.

Now, use a stacking software that allows you to use a single manually shot dark frame to be applied to each frame

If your total shooting session lasts more than an hour or so, you could take a dark frame each hour or so and use each specific dark frame for the images you've taken between when you took the last dark frame and the most recent dark frame. Some stacking software will easily let you do this, others make you work more for it. You might need to create "sub stacks" for the images taken before each dark frame, then stack the separate results of each stack together.

Also, cover the viewfinder if it is a DSLR with an optical viewfinder. Sometimes minute amounts of light can leak around the edges of the mirror when it is up.

If you have a mirrorless camera with an EVF, you do not need to bother covering the EVF.

For more, please see:

What's the best way to deal with hot/stuck pixels in long exposure night photographs?
Why does my Canon 700D take so long processing when I take a long exposure?
Stack of 4 seconds exposure photos of Milky Way, how is it done?