After playing with various numbers of lines I came to conclusion that 20 lines works the best for me. I mean, I'm not trying to outplay the house this way, it's just a more pleasant experience for me personally. I know that with 1 line you can potentially get higher payouts, and, on Dice, for example, I usually play with 100x and higher, but with Slots it's different. The animations and the sounds that come with the winnings are so good to see and hear that I want to have as much of that as possible.
Playing with all 20 lines gives you more chance to win something back although the payout is smaller than when you play with less lines.
When I played the slot game, I usually play random lines. Sometime I use 20, 15, 10, 5lines but my favorite is 15.
The same as you, because I got better result on 15 lines while you got better result with 20 lines.
Of course, its all about luck no matter how many lines we used, then luck will be the main factor of our result.
Yes, of course luck is the main factor, and if you are lucky enough you can win a good payout even when playing with 20 lines, like I just won, for example:
It's funny how my game goes on on Stake for the last several days. I lose on Mines, because I'm hunting for extremely high payouts, like 49,031x and above, and then I win it back, at least partially, on Slots.
And I already have made thousands of bets in the pursuit of 5,148,297x on Mines. Hope I'll hit it one day. 
. Wasn't that amount enough for him ? Why he did took more risk and lost all of his earnings 
