What's the resolution time for a highly qualified German visa?

Visa considerations ALWAYS depend on your nationality. Having a student visa in Spain doesn't change the fact that you are Mexican, which is of course not an EU member. Thus you need to get a EU Blue Card. One has to have a recognized academic degree in a field or 5 years professional job experience.  Then one needs to get a job contract or offer paying a minimum salary of 50,800 Euros a year or 39,624 Euros for a profession that has a deficit of qualified people available like math, architecture, engineering, medicine etc. Being the world best expert in Mexican history for example won't help. Even dentists are not getting Blue Cards as deficit professionals these days because there is no shortage.

The other thing is that even if one fulfills any requirements, the processing time depends on the people taking care of the visa. Are they understaffed etc.? At best, one could only speculate. The best thing is to simply ASK! Contact the German consulate services and ask. If one fills out a request form for a visa then it is only reasonable to ask for an estimation of the time it will take.