15 is more than enough. You finish Fallout 1 with like 5 perks.
bethesda brought the series back to life in a major way with FO3 and even though it had lots of flaws like too many skill points etc, it was still a much better game than fallout 1, and new vegas will prob be better than fallout 3 and fallout 4 will have improvements over FO3 and NV ,thats how i see the game going, but i wouldn't use fallout 1 as the Gold Standard. 5 perks is fine if there is only 10 or 15 to choose from, but there's gonna be 30 or 40 to choose from probably, so 5 would be kinda low, i think 15 is a good amount of perks, it just all depends how effective the perks are, they're gonna try to balance the game and hopefully it will be improved over FO3. but just because something was or wasn't in fallout 1 doesn't mean it should be exactly the same in new vegas, 5 perks sounds kinda low actually, i'm glad fallout 3 had more than 5 perks.