What is the religious ruling on a 35-year-old man marrying a widow 15 years his senior, given his mother's rejection of this marriage, and is he obliged to obey his mother in this matter?

If you are unable to convince your mother to marry a specific woman, and you fear losing your mother, then it is obligatory to obey her by not marrying this woman, unless you fear falling into zina (unlawful sexual intercourse) with her. Obeying one's mother is obligatory, whereas marrying a specific woman is not obligatory. Ibn al-Salah, Al-Nawawi, and Ibn Hilal have explicitly stated the obligation of obeying a parent if they prevent their son from marrying a specific woman. However, if there is a strong presumption of falling into the forbidden, then warding off this evil takes precedence over obeying the mother. It is advisable to prioritize reason and seek a woman other than this one, one whose religious commitment and character you approve of. It is preferable that she be a virgin and of an age that allows for childbearing, in order to achieve benefits such as pleasing your mother, preserving the family unit, and having offspring. And supplicate to Allah frequently to inspire you with what is right and proper.