unprotected intercourse

If we only have sex for 15 seconds, can i still get pregnant?

my period is due any day now. and about 10 days ago me and my boyfriend were fooling around, and he put his penis in me only for about 15 seconds. i know there is sperm in pre cum and thats why im scared. is there a big chance i could be pregnant from that? he's not very worried.. but i am. i havent been getting as many signs for my period as i usually do.....