"Can a woman get pregnant 5 days after her period?"
It's possible, but not likely since ovulation typically occurs 14 days after the first day of your period. Of course, that all depends on the length of your cycle and whether your periods are regular. You might want to do a search on fertility and ovulation.
"I heard that 15 days after your period if your man penetrates inside you you cannot get pregnant."
That's not true because as I said, that is most likely when ovulation will occur. You will be less likely to get pregnant during the luteal phase. Like I said, do a search. There is a lot of info out there.