WTF I dc for like 15 seconds then reconnect then stomp the enemy team then LOSE LP WHEN I WIN????

Ok, WHY DID I LOSE LP WHEN I WON THE GAME? I DCED FOr LIKE 15 SECONDS CAME BACK AND STILL STOMPED THE ENEMY TEAM. WHY DID I LOSE LP WHEN I WON THE GAME???? Could I please get my lp back if thats even a thing that riot does idk. Edit:+19 on top of the +16 if you guys do decide to refund me lp and dont mind because im trying really hard to get back to plat 3. Edit 2:15 seconds isn't an accurate number as I thought, but 45-50 is, but still, I should not be losing lp when it is way beyond the remake period and I come back and smash them