if you change it yourself every 10,000 (not the recommended schedule) you'll get three changes every 30,000 miles for an expense of around $20 bucks.

If you flush it once every 15,000 (not recommended schedule) then you get complete fluid change 2x's in 30,000 miles for around $100.

If you do the recommended change every 15,000 miles then you get only 2 changes for around 12 bucks.

I say change it every 10,000 miles.

You really shouldn't wait for the fluid to burn (turn brown) before changing it...you will cause damage that way.

noel