Honestly, this reminds me a lot of my uncle's marriage. My mother and her siblings were raised as Orthodox Jews, where Judaism and Jewish holidays were an important part of life for that generation. My mother and her sister both married Jewish men, my mother raised us as Conservative Jews and my aunt raised her kids as barely religious Jews.

My uncle on the other hand married a Vietnamese woman, who was not religious, having been raised with some combination of Buddhist and Catholic teachings.

For my grandparents, it was important for their new daughter to go through the ritual of conversion. In Judaism without documented evidence of your parent's official Jewish Marriage Certificate (Ketubah) you are not officially a Jew and might have hiccups marrying an orthodox Jew or getting Israeli citizenship.

I understand my Aunt had various reservations, similar to OPs, about going through a conversion ceremony that she didn't genuinely feel connected with. However she went through with it so her children would get the legal benefits of having parents get an official Jewish wedding.

Fast forward 25 or so years after their wedding, they are still in a loving marriage together. Their house is not kosher, they aren't overly religious at all. They have two children, both well adjusted college graduates who were somewhat exposed to Judaism in their youth but by no means indoctrinated.

And every year my entire life my Aunt has attended our Passover Dinner and Rosh Hashana lunches. She never had to go all in and truly study the religion or be religious, but part of being married is doing shit with your spouse's family that you wouldn't normally do.

My dad (divorced parents) is an ethnic Jew that practices Buddhism and every year goes to Christmas Mass with my step-mother. He doesn't by any means accept Jesus Christ as his lord and savior, but it makes my step-mom happy and makes her parents happy.

I don't know all the tenets of Islam, but as a Jew I've been told that belief in God or complete devotion to the Torah is not necessary at all when it comes to being a good Jew. If you are in the United States I bet you could find an Islamic Congregation that is similarly accepting of converts who might not fully buy into the religious dogma.

You are right that it will be expected of you to attend religious ceremonies a couple times a year, but you most likely won't be expected to go to mosque. You won't have to avoid pork when you aren't with his parents, you won't have to dress conservatively when you aren't with his parents.

To me converting for show isn't a big deal, and is a kind gesture towards your in laws.