Canadian operator Rogers has listed on its website when it expects to receive firmware updates for various handsets. This includes the Sony Xperia series where it flags that the Xperia Z3 will receive the Lollipop update in March 2015, whilst the Xperia Z1 Lollipop update is expected to arrive during April 2015.
Obviously, generic firmware versions are expected to be released earlier than this. However it gives some indication when handsets other than the Xperia Z2/Z3 may start to receive the update. Sony has said that the Xperia Z3 update will start seeding this month, so as soon as we hear any news on that front we’ll let you know.