Licensed Dvd To Spanish Company: How Much Tax?

My video production company here has licensed a DVD production to a company in Spain.

The Spanish customer has witheld 15% tax on the advance of 2000 euros. They say 15% is a reduced rate because we have proven that we pay tax in Thailand.

Does 15% seem correct?

How much would they withold if our company was in the EU?

Will we be able to avoid corporate tax on this in Thailand because we've paid it in Spain?

Thanks