Frankly speaking Biggie, the R 15 is a joke. It would have been acceptable if the price range had been around Rs. 50,000 to 60,000 but a price tag of over 1,00,000 is too much to digest. If the bike had been a 250 cc then it would have been OK but for a 150 cc. Now coming to the point i.e. tyre. Its a pencil tyre. Yes, the size of the tire does effect the performance. The World Wide Web has forums and sites full of debates on this subject. I am posting some links for your reference.
Front Tire Skinny vs Fat tire - TWT Forums
Mazda6Tech - Are Wider Tires Better?
What's the largest size tire I can fit in my Xterra? - Automotive Forums .com Car Chat
Will post more later.