Glide ratio of 22:1? Where'd you get that number from?
V2+20???? 24K motor, 140,000 lbs, Flaps 5 V2 approx. 145 kts. Flaps 15 V2 approx. 140 kts. Using your technique works out to 160-165 kts when the actual L/D glide speed is 211 (QRH).
Other techniques for computing basic L/D glide speed (actual speed is in the QRH for dual engine failure) -
GW + 70-75 kts (+75 light, +70 heavier) -
140,000 lbs + 70 = 210. QRH speed is 211.
120,000 + 75 = 195. QRH speed is 195.
Or Vref 30 + 65.