I don't know if it is really required every 15kmiles, but I would say that at 30k, you probably need it. I went over 75kmiles on mine, and it could have been a lot more because the previous owner didn't look like the maintenance type...like I am?

I found 3 of the 4 intake valves, which should be set at .004 inches, had absolutely no clearance. All of the exhaust valve were about .004, also way too tight (spec'ed at ..012). The car was having cold starting problems last winter.

The car runs and starts a lot better. Fuel economy went from 25 to 30, and now is running about 32 with the addition of fuel conditioner (power service).

Do a search on valve adjust and you'll find a lot of info.

Joe