We normally consider that a depo does not offer you contraceptive protection twelve weeks after the injection, however in practice it can take many months for cycles to return to normal. If your cycle does not return to normal 12 months after the injection then you may need further investigation.
is it possible this person can get prego from pre cum with only 15 of insertion
Yes, any contact with precum could lead to pregnancy depending on when the female partner ovulated.
i meant inserted for 15 secs and she was on the 6th day of her cycle that last 28 days
Sperm can last for up to 5 or even 7 days in some cases, so as the contact was before the usual fertile time then we cannot say that the risk is zero.
There is a potential risk that she may have ovulated at day 10-14 and sperm could have fertilised the egg.
Always use a condom if you do not want to get your partner pregnant.
does pre cum have the same intensity as a orgasm of semen
It will contain viable sperm, but no way to be sure of quantity in a specific individual without sperm analysis.
if you wipe it off and make sure its gone can u get someone prego with 15 secs of intercourse
There is no way you can be sure that some sperm did not get left behind. Sperm are very very small. It only takes a small quantity.