bdesmond's theory is correct but isn't the power draw in this case about 9.5A (he is only loading the
dimmer with 1150W).
Although, having said that, the tolerance of the breaker may not notice the difference. Most breakers will allow some current draw to sit above the threshold of the breaker for quite some time before tripping and given that you can get a few hours before tripping, that seems to be the case here.
Ampacity – Have you checked that there is nothing else running on the same
circuit as that will certainly contribute to your problem. Is it possible that the breaker could be faulty? Have you tried running the dimmer off another circuit? This information would be very helpful.
Given that you are close to the limit in what you are running, I would certainly follow bdesmond’s advice and limit your intensity. I very rarely push my fixtures past 80% as the visible difference is negligible (in my opinion).