Glam
I would suggest that Longhaul aircraft require about 8-9 crews per aircraft and shorthaul about 4-5 crews.
Using your figures 15x8 (or 9) crews = 120 (135) cabin crew per 747 stood down and say 6x4.5 = 26 cabin crew per 757 stood down.
What is it? 8 747's and 6 757's? If so about 1000 longhaul cabin crew and about 150 shorthaul cabin crew. Note - this assumes the same number of crew on board going forward. The numbers in surplus increases if the number on-board decrease.
Just ballpark numbers ....