Is it obligatory to obey one's parents and forgo marrying a righteous, non-university-educated girl, or should one insist on marrying her despite their refusal?

If the girl is religious and well-mannered, try to convince your parents with the help of Allah, through supplication, and by seeking assistance from people of wisdom. If they refuse without a valid Shar’i (Islamic legal) reason, then you are not obligated to obey them, especially if you fear discord (fitna). If you prefer to honor them and forgo marrying her, Allah may compensate you with someone better. Fulfilling a promise is commendable, but you do not sin by breaking it. Material and social differences are not considered in compatibility (kafa’ah); rather, compatibility lies in religious devotion.