Confirmed. Sega is not coming to E3 this year. Sega IS going to have a booth this year, but there won't be anything related to Sonic.
E3 is one of these big conventions in which new games are announced, and it will start from June 16th till 18th 2015! But here's the catch:
SEGA so far has not registered their name in E3's website . With two months away, the probabilty of them appearing is unknown. They may or may not appear in this years E3.
Possible reasons for this is because of the negative reaction of the Boom Games, and their recent big changes of their plans. If they are not there in this years E3, then Sonic Runners could be the only Sonic title for this year. Sonic will be coming to home consoles, but nothing much has been revealed yet...