@pete-pjb you’ve been super helpful with this, and I think even with your limited knowledge on the Teensy/Arduino platform you still know more than I do ! 
I’ve been able to shave off a few more kilobytes by doing the following in all of my font files:
I’m now down to 60% RAM usage - that’s 13% less than before! and flash is only at 6% usage = 550Kb out of 8 megabytes!