I'm used to watch raptors with my 15x56.
I never scan with these binos.
I watch with my eyes first, try to locate the raptor (to get an idea of his speed and direction), stay focus on him, then bring the 15x to my eyes.
That's great if that is how you find your raptors, but if I relied on my eyes to find raptors first, I would find very few. I would say maybe 90% of the time I am looking for raptors, it is with my eyes in the binoculars, and the birds are normally 500m to over 1.5km away.
Should you visit London I would be delighted to go to a couple of my favourite spots with you, your 15x56 would be great for some places where they reguarly perch to hunt.