Is 15/40 sprocket size good for yamaha r15 v2.0? Current set-up is 15/47...

hi there is your chain in good condition or worn out ,is the chain dry and needs oiling or is it incorectly adjusted for the bike ,or is the chain out of aliagnment these would all cause noise problems ,or if the chain has been replaced before is it the right size for the sprockets ,and are the sprockets in good condition ,to check if the chain is stuffed move the chain sideways left to right of your bike and if it moves more than a sixteenth of a inch it is worn out .hope this helps cheers

Unfortunately the you are constricted by the width of the swingarm.

The tyre size for the R15 is the optimum tyre size for performance although it does not look as good as chunky tires.

Isn't performance more important than looks anyway though?

Short answer to your question... No, this can not be done.

You are governed by safety. The hub width will determine the maximum width and type of tyre as will the width of the rear suspension/wishbone.
Consult a qualified tyre fitter for accurate sizes. Don't forget your speedometer will no longer be accurate!