It was the same in 2010; Kyiv and Michurinsk were contenders, so CIS-11 was held in Michurinsk. It was the same in 2012; Minsk and Odessa were contenders, so CIS-13 was held in Minsk. In both cases, the reasons were mainly geographical – people wanted to go south.
Therefore, if CIS-15 isn't held in St. Petersburg, but CIS-16 is, no one will suffer.
In fact, it might even be better for me; I'm skipping CIS-15 even though it's in St. Petersburg.