Prepaid surfstick slow on my macbook

Sorry, I don't speak german yet. I bought a prepaid surfstick with a 25,- load. To surf?...it works on my imac but it's unusually slow on the macBook (4 years old). Any help will be appreciated (O2 can't explain it).

Thanks

if you have any solution you can answer me on my personal e-mail :deluxeamp@wanadoo.fr