I am kinda unhappy about this. UW Madison is academically my top choice among all the universities I got in, but it has offered the least amount of financial support. Other grad schools are offering at least 20k and most of them have health insurance and 4-5k of fellowship. I talked to a current student at UW Madison who is working 50% (20hrs) and is making roughly $1500 a month, and this hardly leaves any time for additional work. But the student said that the rent ($500ish per month) and the living costs are cheap so it is a comfortable living, even if you are not saving lots of money. I would definitely ask around more people if it is easy to earn a bit more because 15k seems too little
I'm not sure if it's any different for international students, but I calculated roughly $1300-1400 in monthly take-home pay considering the $15,342 stipend, 20 to 30 hours per week in part-time work during the summer, and 15% effective tax rate (is this accurate?). I'm told that it's plenty to live on in Madison, though you won't be living large obviously. The main object to consider is what percentage of your monthly take home you can put toward saving or student loans if you have those.