We tried to test it beforehand but it's hard to prepare for such a number of users :) We've launched just 3 weeks ago. If you leave the site open it loads after a while, or you can bookmark it and come back - it's worth it :)
How much load are you talking about? Once it finally loaded for me, I gave up after about 45 seconds. I suspect you're doing some really cool things on the backend, in terms of checking permutations of flights and wiring together the cheapest rates. Still, I wonder if you're doing anything with your Angular front-end that really hurting usability.