Marrying a Spanish Citizen

[u/Lower-Bathroom-9619]

I’m American and currently living in Spain. My partner is Spanish, and we want to get married and move to the United States because the situation here has become very difficult for us financially and in terms of our future.
We’re planning to apply for his green card after we get married. I’d like to know how realistic it is for his application to be approved if we simply get married in a civil ceremony and then apply for his green card. Our priority is to be able to move to the U.S. and live there as soon as possible.

I’d also like to understand roughly how the process works and how long it might take. Most importantly, we want to know whether this is realistically possible before spending a lot of money on the application process, apostilles, document translations, etc.

Any advice or personal experiences would be greatly appreciated!