Stick with 15' and use good performance tires. Jazz is already a slow car, don't make it suffer even more!  

for which size?enkei tuning 18 inch can get below 3k lar..around 2500-2600.
if enkei japan only can get 15 and 16inch

If new, usually above rm5k for lightweight ones.

5-6k++ depend on model
currently available in market are rs05rr,pfm1,nt03rr..and few more i forgot the model.

As far as I know (anyone can CMIIW) Enkei doesn't make forged type rims to make lightweight rims. They instead use MAT technology which is still cast type rims but with more advance technology so that it can lightweight yet a bit cheaper than forged type. (Normal/traditional cast type rims are heavier and cheaper still). However not all Enkei Japan rims are made using MAT and therefore not all of them are lightweight.

Rays is said to have one of if not the most advanced forged rim manufacturing facility in the world to produce lightweight yet strong rims, hence more expensive. Similarly, not all Rays rims are forged type, they also make cheaper normal cast type rims.

So in general if I were to rank them, Rays > Enkei Japan. If you know watches, Enkei Japan is maybe like Tag Heuer while Rays is like the Rolex of rims.    Both are excellent luxury watch brands and both are expensive but of course Rolex is still the king.