I looked up the ip 107.22.61.99 at http://tools.whois.net/whoisbyip/, which didn't really tell me much that I didn't know. Its a dynamic ip controlled by amazon aws. It possibly could be a crawler, because the ip is similar to several found here:
http://user-agent-string.info/list-of-ua/bot-detail?bot=CCBot
I think on the sites I manage I have it set to a little higher than 15 for crawlers, and then I throttle the connections. I wouldn't be really worried unless I saw it start to hit the wp-admin page or known vulnerable url's (check the box to auto block people who hit that).
tim