Upgrade Tire for OCBC Race

next week will be the OCBC Road Race. I will be participating the 40km race with my mountain bike. As my current tire is almost wore out particular the rear wheel (should have do a tire rotation similar to that of car) so I decided to upgrade my bike tire to a 1.5 instead of the current 1.95. this 1.5 will be better for road as it is slimmer. haha...

the bike looks a little not in proportion with this slicked wheel.