No,you aren't the worst gambler (for now). You made a good decision to stop even though you already lost your 10 btc and still hold the rest (15 btc).
You and we always have the reason why you/we must continue this live, there are still your parents, your brother & sister, wife and your children (if you already got married).
Here is an example of a gambler worse than you, he lost 360 btc just in some minutes...
I agree you are correct because there is even more worst gamblers just like the one you exampled .In the OP ,gambling will don't kill you if you have no money. You can earn back and earn more money in different ways .Lucky for you that you stop at losing that amount 15btc is a big enough to start and value what you have ,Do some but not to think again to do gambling as you knew already what can possibly happen again.
Suggesting him on playing again next time would not really be good because the 15 btc he had left would have the risk on losing it all because chasing loses is really be very bad instead on minding on how to earn those loses then better to stop completely because if you let your emotions control you then you will really suffer even more 10 btc is huge but losing again 15 btc left would hurt even more.