A speed of 1500-2000 g for 5-10 mins should be enough to pellet your eukaryotic cells, as for bacteria it is around 4000-6000 rcf, 5-10 mins I think you should give a try.
Speed depends on the radius of your rotor (both Léa and Stefan addess this). 1,500 G for 5 min seems about right. The alternative would be to filter, say with a 1um pore size.
In my experience a contaminated culture is a culture to be discarded. Neither filtering not centrifugation are likely to rescue a contaminated culture.