I'm confused. What question are you asking?
If you're asking about whether or not its normal to have to re-hydrate your yeast, I think its personal preference. I have done both when it comes to dry yeast. There were some that I just sprinkled on the top of the wort, and there were others that I re-hydrated. Each time I have re-hydrated, it sounds like what you described happened to you, so I'm going to say that its normal. If I had to venture a complete guess I would say that it's because yeast used in brewing takes longer to start really working. Think about when you make bread, you see the bread start rising fairly quick. In brewing, fermentation can take a lot longer to start. So I would assume that you didn't see much action when you re-hydrate it because it was only 15 minutes.
If you're asking whether or not you should be seeing more bubbles in the airlock, first read this: Link
. And second, remember that bubbles in the airlock are just a release of extra CO2 and not necessarily a sign of fermentation. Fermentation can be happened inside the bucket without moving the airlock.
My vote is to give it a week or two then get a hydrometer reading. Until then: RDWHAHB