Does someone has any suggestions how to make 17 BTC with 7 BTC starting capital in short period of time?
I think that you can try to gamble with them because that can earn you some quick Bitcoin but the chance of winning is not big so now what can happen if it goes wrong.
If you do not want to do that then you would have to use your own money.
Gambling is not a way of growing money, it is a game for having some fun but not a source of income for anyone, only a few people get lucky and get good returns with it but that does not apply to all, so don't be mad and spend such a huge capital on gambling.