yeah but my cousin has a 2 gig sd class 2 and his load time ist 10 seconds?
2GB SD cards don't have classes, the class system was introduced with SDHC.
For older non-SDHC cards it varies depending on the card, there is no standard for read/write speed so the card could be either fast (like the Japanese Kingston cards that were so popular for DS flashcarts back in the day) or slow, and the only way to tell would be to benchmark it. The card is probably still much slower than a UHS-I card.
But that is probably a moot point as I doubt the Wii's SD reader is able to take advantage of UHS-I speeds anyway. So most cards would probably perform about the same on the Wii. Not sure why your cousin is getting so much better load times though. It is possible that there's a hardware difference between your Wii and your cousin's that caps the SD speed at a lower rate on yours. There were multiple hardware revisions to the Wii but I have no idea if they changed the SD reader.
Have you tried loading from a USB HDD? I expect it will be much faster. I would suggest just going that route instead as HDDs are cheap and a large enough SD card to fit a significant amount of games on is not.