You would need around 8,376.98zł (1,613.81£) in Warsaw to maintain the same standard of life that you can have with 2,700.00£ in Leeds (assuming you rent in both cities). This calculation uses our Consumer Prices Including Rent Index.
1500eur per month for apartment in Warsaw for 3 people? I think you can find something small quite easily for 1/3 of that. 9000pln - is it net or gross?