I have a dryer exhaust that goes into an interior wall and comes out about 10 ft away in an exterior wall. I assumed it ran below the foundation with a couple of 90s.

Well long story short, on n unrelated project I discovered it actually runs up, over, and then back down again. So 4 90s and about 25 ft. To top it off it is made from 3 inch PVC.

Right off the bat, I'm dropping 2 90s and 8 ft of length by exiting the exterior below the 2nd floor, but I'm debating ripping it all out and starting over because of the 3 inch PVC. It's a 25 year old slab house, so below the floor isn't an option. To get it all done I'd have to rip out a bunch of drywall and use one of those oval vents because the 4 inch vent doesn't fit inside the interior stud wall.

Anyone see anything like this before? Is this a fire waiting to happen or it lasted this long, shorten it up, clean it good, and call it a day?

With that length and that many 90s, you'd need a booster fan. IRC max lenght is 35 or 40 feet, can't remember which. Every 90 counts for 5 feet, every 45 is 2.5 feet.