I've seen reports at least one of the F-15s exceeded mach. Is that usual in these type of intercepts?
In a real active air scramble like this event, the fighters were most likely directed to get there ASAP, considering the magnitude of the possible threat. From Portland to the Seattle area, it would be a short flight over the Mach. It’s approximately 113 miles from Portland to Seattle. At Mach 1, 10 miles per minute is covered. If it were me, and the command authority directed ASAP, I wouldn’t be doing only Mach 1.
“Usual” doesn’t exist during an active air scramble.