The Nexus 7 2012 3G has skipped both Android 5.0 and Android 5.0.1, instead it got updated directly to Android 5.0.2 Lollipop firmware LRX22G which takes up more then 400 MB. It seems like Google is rolling out the latest update for the Nexus 7 2012 in phases and it might take some time before you can upgrade your device OTA but you can check if it is available from Settings > About device > Software updates > Check now
Android 5.0.2 OTA For Nexus 7 2012 3G
If it isn’t available, there are other ways you can upgrade Nexus 7 2012 3G to Android 5.0.3 by downloading the OTA .zip file here (Mirror) It is important that your Nexus 7 does run Android 4.4.4 KitKat as it is required in order to upgrade manually to 5.0.3. If you want to know more about the changes made in Android 5.0.2 make sure to check out the full changelog of changes.