I had sex before 15 days of period? I am in depression plz help me!

Pregnancy

Hi there,  Was there protection used in meaning a condom?  15 days before your period is usually midcycle....so if you have ovulated and no contraception was used there us a higher chance, in saying that it doesn't mean that you are.  Anytime a couple has sex without protection there is always a risk of pregnancy or STD.  There are pregnancy tests you can buy that can detect pregancy a week before your period, you could always try that to ease the nerves. 

It was unprotected sex but i didn't cum inside her... so i need to worry or not?

It does not mean that you have not impregnated her. The only way to find out is by a pregnancy test. 

After how many days she have to check?

Some pregnancy tests don't show until a couple days before her period, however there is a brand that can early detect as early as...5 days before.  Unfortunately even though you did not ejaculate inside her, this doesn't rule out the chance of pregnancy, although less likely, there can be pre ejaculation which can not always be felt.  I would try and relax until you know either way.  There is nothing you can do at this point.  One thing you can learn from is before engaging in sex you need to be prepared, buy some condoms, keep in mind they are 98% effective meaning it could happen, but less likely.

No she would not be able to.  It sounds like you both are not experienced in this area, I would suggest once you both get this figured out, you talk to a health counsiller in regards to birth control options, and preventing STD's.   Then once you resume back to having sex you will both be more prepared and not have so many anxieties.