I tend to lean toward a very strong FALSE. At economical cruise a 25% reduction in IAS would put a whole lot of aircraft at just about the pre-stall buffet margin or worse. The best option for is to avoid the turbulence. If unable, maintain turbulent penetration speed as published for the airframe at given altitude. Disengage altitude hold and allow some variation in altitude. Frequently a strong updraft is followed by a strong down draft. Remember to let the ATC know what is happening.