The shoe is much bigger than the 1.5s.  I have about 5 or 6 pair of the 1.5s.  I ran in the 2.0 after getting fitted at an Altra booth at the Boston marathon and developed bursitis of my ankle. Realized the shoe is slightly taller and because if the loose fit it was rubbing against my medial ankle bursa. Wish the salesperson fit me down a size. I since rested, healed and bought the older 1.5 and have been fine. Haven't tried the 1/2 size smaller yet.