Here is 400% FPL, I have a hard time believing many families just over these limits are paying full tuition for all their children. Anyone with more than 3 children making this income is going to have a very difficult time paying $15k per child.
Family size 2022 2023 income numbers
For individuals $54,360 $58,320
For a family of 2 $73,240 $78,880
For a family of 3 $92,120 $99,440
For a family of 4 $111,000 $120,000
For a family of 5 $129,880 $140,560
For a family of 6 $148,760 $161,120
For a family of 7 $167,640 $181,680
For a family of 8 $186,520 $202,240