It sounds like this won't be a replay of previous H!P group's Full Chorus appearances put into one special.
Full Chorus site says all groups (except for C-ute) will all be guests on the show and perform their latest songs in full. It also says Kobushi Factory will be performing too. Kobushi Factory has never performed on Full Chorus before.
MC Hama Okamoto, (who was absent on Morning Musume. '15's first appearance) will be there. He is a big fan of Morning Musume. '15. They will also discuss Fukuda Kanon's graduation too.
http://www.bs-sptv.com/fullchorus/