I think one question that is of importance here is the following. Try to keep company names out of this, because it is not useful or helpful for the debate. The ones who work there will know, the rest can guess, but this is not important.
Person X, has worked with the company for more than the 15 months required, and deducted 1000 Euros from his pay every month in addition few more months training period where the pay was pocket money only!
The additional "bond" is work requirement, to stay another 21 months and work if not they will penalize you with another 15.000 Euros to pay if you leave early. At to the fact, a completely one sided contract which states if you leave before the 3 months notice period you must compensate the company with 10.000 Euros.
One sided and unbalanced, as it does not say they must compensate you if they end your contract with less then 3 months notice period.