That's why u should take 3 potions instead of 2 charge you'll get more health back with 3 potions. And once you'll back u might need only 1 or 2 extra pots till u have enough sustain (life steal and heath regeneration)

If u are lvl 15 u shouldn't play jungle cause jungling without runes is a pain on the ***. I would recommend you to play him top u won't struggle as on jungle.
But play where u want it should work out but u have more chance to succeed as top and it is even easier to learn.
Anyway have a great day cya.

Thank you for the reply :) yeah, i underestimated Bounty Hunter ^^" i'm a beginner with rengar (especially as a jungler). Btw, don't you think the refillable potion is better than the healing potions in the early game ? Maybe at higher level people help more the jungler, but at mine (~15) it's often hard to start without any help :s

It's simple.
Of course u can take Oppressor cause of the E but Oppressor gives 2,5% bonus damage IF the ennemy is CCed meanwhile Bounty Hunter gives 1% increase damage every kills u do no matter if there is a cc or not.
Do the math and u'll see that after 3 kills u'll get 3% increase damage when the Oppressor will still give u only 2,5 IF CCed.
That means that after 3 kills Oppressor is already outscaled by Bounty Hunter.
U can take Oppressor if u want to do a lvl 2 gank or very early invades.
I would say that Oppressor is situational.

Hope you understood. Thanks you for asking tho. :D

I just wanted to know something : why are you using Bounty Hunter instead of Oppressor for the masteries? Oppressor is really good in my opinion with Bola Strike.