Betta Fish: My mom doesn’t want to get him a bigger tank.

I got this guy a few hours ago, still trying to figure out a name. But me and my mom got a 1.5 gallon tank because we didn't want to spend a lot of money. But I’ve been looking online and it says I should get him a bigger tank. I asked my mom about and she said she won’t get me a bigger tank for him. She said something along the lines of “I’ve had a lot of betta fish in the past and this is the biggest tank I’ve gotten for one. Compared to the container he was in at the store, this is paradise to him.” I just really want to get him a bigger tank so he can swim around and stuff but my mom doesn’t want to get one.