Thanks for your comment!
It's been a while since I've tinkered from Unity, but from memory there are couple different places you can affect animation speeds for tiles. Easiest way is to adjust the animation frame rate of the entire tilemap (just double check your tiles are on the correct tilemap if it doesn't appear to change anything). You can also change the frame duration of the animated tiles one by one.. Could be a bit tortuous that way but possible.
Here's a video showing the two different ways: https://youtu.be/6JXAAsVIVbs?t=324
I'm not a unity expert by any means, so hopefully that helps!