I assume that the recommended upgrade path from 1.5 to 2.0 will be :
1.5.x > 1.5.latest
1.5.latest → 1.6 latest
1.6 latest → 2.0
so you can do some work upfront and update to 1.6 first 
I assume that the recommended upgrade path from 1.5 to 2.0 will be :
1.5.x > 1.5.latest
1.5.latest → 1.6 latest
1.6 latest → 2.0
so you can do some work upfront and update to 1.6 first