If you go into the System section of your online Sonos account your products are listed. Any that are eligible for upgrade will be marked as such.

For supporting evidence, gen 1s usually (possibly always) have a mute button, gen 2s a play/pause.

Before the serial number on the label are 4 digits in format YYMM. It is believed that 1502 (ie Feb 2015) and later are gen 2.

See if that all ties up.