Would this method be able to generate signficant income for the mages?
Yes, it would. In a time when electric power was unknown, this would be the only viable way to have ice made easily available for many latitudes. The ice trade would start a few centuries earlier.
Ice created by magic would help preserve food anywhere in the world. Just this alone would be a major revolution. It would change the economy for food markets as well as for nautical exploration. Seriously, go read First Voyage Around the World by Antonio Pigafetta. After months onboard sailors would trade a king's ransom for a dead rat because it was the freshest edible thing available.
Ice has other uses as well. Medically, it can be used to treat rash and first degree burns, for example. Doctors would also use it to fight fevers. Barbers could press ice on a client's cheek after removing their teeth (barbers were the dentists of the past).
Gastronomically, asides preserving food, it is used in the making of ice cream. Ice cream is as old as the ancient romans, but you had to climb a mountain or wait for a snowy winter before the ice trade became a thing in the 19th century. If you think this is silly, remember that during the crusades people would kill for a pint of sugar.
People would find other creative uses for ice. If you want to take water upstairs, for example, you have to move the weight of the water + its container. With ice blocks, you don't necessarily need a container. And if you need to move heavy furniture around, perhaps placing it over a slab of ice makes things easier.
So long story short, I think not only the mages could make a living, they would be wealthy, upper class citizens.