do i assign 15 access point to each WLC?e.g 15 LWAP per controller?or what?
Whatever floats your boat. If I was in the same situation as you, I'd have 15 LAPs go to one controller and the other 15 to another. I would also configure the backup WLC as well.
2) is it recomnded to ulize both gig interface on the WLC?e,g 1 interface to each 6506?
It would be nice but not necessary. Cisco recommend no more than 25 APs "tied" to one distribution ports due to bandwidth constraints. Since you have a 4402-25 I don't see any need unless you have extra SFPs available.