I can't venture much of a guess, but I do think 1.5 tons seems too low.
I don't know how many people are financially supported by the Busse shop, but I will conservatively guess >3 (Jerry, Jennifer, ?). If those 3+ people are going to live anywhere above the poverty line, then I think the shop must be producing a lot more than five knives per day.
Let's very conservatively estimate that the Busse shop makes 5 knives per day, at an average of 1 pound of INFI each (less than a SH or BM). At that rate, they'd go through 1.5 tons of INFI in well under two years.
The actual figure must be at least several times higher than 1.5 tons, or they'd have been driven out of business, by now.