I often run into this problem, and here is what I do. I modify them…
Here is a 201Z Cutter that I use for deep slots and cutoffs in 2x4s… you can see that I relieved the shank down to allow for some clearance (so it doesn’t rub)
Here is a 2mm cutter that I modified to cut deeper when I was making a stainless steel watch (body)
How I do it: I own a few cheap Chinese Diamond ($15) grinding wheels, and I place the cutter that I need to modify in a cordless drill and grind it while spinning the cutter. It does NOT need to look pretty…it just needs to be a little smaller than the cutting diameter.
NOW to cut 22mm deep with a 1.5mm cutter…that is REALLY deep (Greater than 10 times the Diameter (10D)). I would do that in steps. Start with a standard cutter as deep as it goes, then another cutter with a relieved shank to (about) 10D, then 15D.