Actually there’s reward in battleground if you are loosing.
You usually need to loose and get a great performance in the battleground to get it.
I merely got it 75% of the time, but when i die very often in a battleground or i perform bad i don’t get the steel strongbox.
I noticed if you joined a game already started and you loose you got way more chance to get the Steel Strongbox.
Here is the reward if you perform well meanwhile you have lost :
it usually give between 129 - 71 golds too.
The reward when winning ( whatever your performance ) :
it give between 229 - 171 golds.
So my opinion on this is i think the reward is fine, but i think the malus of leaving a battleground must be highter than just 15 minutes because people leave like ashran in WoD without malus and they can reconnect to an another character or doing an another thing since 15 mn is nothing in term of " punishement "