Thanks All my fellows on PWs. For now I am not going for the rim change. I consulted two of the major Service centers and my family mechanic. All of them have the same opinion as imranbhatti, vickytulla, ammarzahid also mentioned. 17 inch will effect Sprinter performance a great deal. It will get lower from the rare which will be a factor in less road grip. Also engine ground clearance will become lesser. Reduction in top is obvious. And If put a bigger 17 inch tyre then it will not help me greatly in avoiding the fender.
Anyhow, the tweaks I have already made are enough for now, the actual problem was the weak chain sprocket set. Due to weak chain, I had to get it tight many times resulting in tyre to be near to the fender tail.
With fresh sprocket set, the issue has been resolved.
If there's required further improvement then the latest mudguards available in the market can be installed. The new mudguards are redesigned and are more away / straight / more pointing outside from the tail.
Feeling happy as I satisfied once again with my loving ride