The amount of money you can make by selling 15 servings of pig's feet rice depends on the cost and gross profit.

For example, if the cost of pig's feet rice is 60%, then the cost of a serving of pig's feet rice sold for $15 is $9. This means that for every serving of pig's feet rice sold, a gross profit of $6 can be earned.

However, if the cost of the pig's feet rice is 70%, then the cost of a serving of pig's feet rice priced at $15 is $10.50. This means that for every serving of pig's feet rice sold, only a gross profit of $4.5 can be made.

The exact amount of profit therefore depends on the cost and selling price of the pig's feet rice.