I started swimming and trying to swim 1500m nonstop (as a first goal). I gradually increased my set distances. After 4 weeks I can swim 1000m nonstop. I guess I will reach 1500m in 2 weeks. One thing I observe is; my stroke count per 50m decreased from 59 to 48 in 3 weeks period. But stopped there. (I can swim 1:52 100m) 
Is 48 strokes per 50m a good rate or should I try to lower the stroke count by lengthening the stroke length?