Mac Yosemite Airdrop is very slow
I've noticed the same thing when I connect to a hotspot after upgrading to Yosemite, and to a lesser extent any wifi network. It seems to be an issue of new software issues and the wifi max speed.
Workaround
Option-clicking on the wifi icon and selecting Disconnect from <Network name> will disconnect you from your current wifi network, which has tripled or quadrupled speed for me when starting a new transfer. This works best when both computers are disconnected. It kind of sucks, but when you're transferring files in the hundreds of megabytes as I was, it's worth it.