You're not slowing an airliner's KIAS by 25% at cruise.
Speed range ('window') between low speed 1.2 margin and redline at cruise altitudes is frequently 30-50 kts. Mach changes of .01 is a small amount of indicated airspeed (3-5 KIAS). KIAS is 250-300 KIAS. That means the 'window' speed range is approx. 15-20% of KIAS.
Actual cruise speed is typically about the mid point, or slightly faster, of the 'window'. So typical cruise KIAS is about 15-25 KIAS above the 1.2 yellow band ('hook'). So the speed available to reduce by, while staying above the hook, is maybe 9-12% of KIAS.
KIAS speed reduction from typical cruise to 'turbulence penetration speed' is more like 1-2% of KIAS.