Hi Lars,
The OS control used to display web content on iOS is a different rendering technology than the OS browser, and has different performance characteristics. In particular it is slower on older devices, such as the iPad 2.
Given your description my guess is your image size is driving the performance issues. Take a look at how big in pixels your images are and aggressively re-compress them. I've had success scaling images to 50% of the size I think I need, and then saving them as JPEG at a 7 (or even 5) quality level in Photoshop.
As for the videos, make sure you're using the <video> tag with a link to the video hosted somewhere for streaming purposes.
Neil