The G4 does have a 3000mAh battery too, which is larger than most phones. That alone can add to charging time.
Though, you do sound like you're seeing a drastic difference compared to what you expected. What kind of charge times are you getting? On a related note, is that with the stock charger, QC2.0 charger, or something else? Also, have you used an app like Gsam or Ampere to monitor the actual charging current? If you use Gsam, posting a screen shot of the charging graph showing the rate of charge over time would be helpful. Once fully charged, how is the battery life?
It is possible that there's something abnormal going on with your specific phone. Long charging times can be related to hardware defects and rogue apps as well.