Is the fiancé entitled to prevent his fiancée from studying at a university he deems to have a corrupt moral environment, and would he be sinful if he did not do so?

Parents must fear God concerning their daughters and keep them away from places of mixing and suspicion. If you have lawfully contracted marriage with this woman, she is your wife, and you do not have authority over her until you give her the mahr. Obedience at this stage is due to her father in what is good. There is no sin upon you if you advise her, and if you have consummated the marriage with her, it becomes obligatory upon you to command her to abandon suspicious places. If it is merely an engagement, then there is no sin upon you, all the more so. We advise you to expedite the wedding. If it is not possible, then continue advising her family and warning against unlawful mixing.