If you just got it and upgraded you will have the latest version. You can check by having iCal in the front, and clicking on the iCal menu (top left) then choose about iCal. That window will tell which version.
So you should be able to see 1/2 hour increments and easily set 15 minute increments. You might want to check out this sight: http://www.apple.com/support/mac101/work/10/ for iCal help and http://www.apple.com/support/mac101/ for general getting started.