How much progress can I expect in an immersion Spanish school?

It depends a lot on your language learning abilities and how your future employer defines bilingual. When you say that you studied Spanish at the University for two years do you mean that you started with Spanish 1, then it is very unlikely that your Spanish is at the intermediate level. If you started at Spanish 2 or above it may be but given what you said about your Spanish experience you are "low intermediate".

In 6 weeks most people can go from low intermediate to advance if 1) they don't spend their free time speaking English with other students in the school, 2) if there is no more than one other student in your homestay and your host family spends time talking to you at meals, and 3) if you seek out practice outside of class and beyond your homework assignments.

Hi there,

it depends to a large degree how good you are with languages. I studied Spanish in Nicaragua and Ecuador last year for almost 5 months (4 hours a day with a private teacher). I did slightly better than most of the other students. I would say that my Spanish is kind of ok, it is easier for me to speak than to understand because most locals speak pretty bad Spanish. My teachers in Nicaragua told me that my Spanish grammar is better than 90% of the population in Nicaragua, however, I am far from fluent.

I fun in Guatemala. I went there 3 years ago to Antigua and really liked it.

You need about 700 hours of classromm teaching and about 2 years living in a Spanish speaking country to be somewhat fluent, and that's a fact!

I live in Southern California and we have a lot of Spanish speaking people here, however, the language they speak is not really Spanish, it is a combination of bad Spanish with a lot of slang.

It really depends on the education of the Spanish speaking native how good or bad he/she speaks Spanish.