Hamilton wasn't happy on Thursday and switched to a bigger wing for Friday that gave the car more stability, but cost time on the straights.
He progressed through the first two qualifying sessions in 11th and 10th positions, and then took eighth when it mattered in Q3, a place behind team-mate George Russell.
Max Verstappen claimed pole for Red Bull ahead of Ferrari's Charles Leclerc.
Hamilton stressed that bouncing was making life particularly difficult in the first part of the lap.
"It wasn't a really good qualifying at all," he said when asked about his session by Autosport.
"I really struggled with the car yesterday, and then FP3 I was really much happier with the car, with a slightly bigger wing, but I was losing two-tenths in the straight.
"But I gained some stability back, and I was I was much, much happier, and I thought I would carry that into qualifying.
"But unfortunately, the bouncing is still there. It makes it very, very, very difficult to push through that for a session. That's why we were so slow in that first sector."
Hamilton conceded that despite the bouncing trait, the W15 has more potential than its predecessor.
"If you took that away the car is really so much better than last year, in every area," he said.
"It's just that it's really causing us some real big trouble. In the second or third sector, we were a lot closer, and we're able to be closer through some of all the rest of the corners, but just that first section – it's the same as last year."
Hamilton said he will play it "cool" in the race at a track that is well known for drama and safety cars.
"I mean, jeez, qualified ninth and eighth, so I've had a horrendous two qualifying sessions," he said.
"Tomorrow is just about being cool. And I'm just going to try and enjoy myself.
"It is what it is, but we're not fighting for the front, for the win. So try and bag as many points as I can."
Mercedes trackside engineering director Andrew Shovlin admitted that the W15 isn't competitive enough and that the team will have to take an opportunistic approach to the race.
"Our performance in the high-speed corners wasn't good enough," he said.
"We improved the car slightly overnight, but we'll need to make this better ahead of Suzuka and Melbourne.
"We don't really know where everyone will stack up on long run pace tomorrow. [Max] Verstappen looked clear of the field, but it's quite tight behind, and not many cars did runs that were long enough to get a clear read on degradation.
"It's normally an incident-filled race here so opportunities may come to us tomorrow. We will look to take advantage of those, but today just wasn't good enough."
