The only issue with a 15 point buy is that it hurts characters like the Monk. The monk really needs at least a 20 point buy to be on par with other classes, the same with any MAD character type.
If you're allowing archtypes, just remember that it changes what the characters can do. Rangers opening locks, Monks shooting bows, etc and that they might not be able to do what you would expect since they had to give stuff up to get the new things. You'll need to make sure they you haven't locked down the game because there's a locked door and you expected the rogue to be able to open it, but then realize that the rogue gave up the ability to get something else.
Also don't assume that PF fixed any particular problem you had with 3.5. They only fixed some stuff and left other problems alone. Make a list of the issues you had with 3.5 and then see if they were addressed with PF. I found that many of my issues weren't addressed and I had to house rule almost as much stuff as I did with 3.5, which made me wonder why I bothered to switch at all (other than the ease of running games with the APs).
If you're allowing archtypes, just remember that it changes what the characters can do. Rangers opening locks, Monks shooting bows, etc and that they might not be able to do what you would expect since they had to give stuff up to get the new things. You'll need to make sure they you haven't locked down the game because there's a locked door and you expected the rogue to be able to open it, but then realize that the rogue gave up the ability to get something else.
Also don't assume that PF fixed any particular problem you had with 3.5. They only fixed some stuff and left other problems alone. Make a list of the issues you had with 3.5 and then see if they were addressed with PF. I found that many of my issues weren't addressed and I had to house rule almost as much stuff as I did with 3.5, which made me wonder why I bothered to switch at all (other than the ease of running games with the APs).