Is it charging from dead to full in 45 min? If so, that could mean the battery is bad because a good battery should take over an hour even when Quick Charging.
If it's already at something like 50% charged when you plug it in, then yes 45 min could be expected.
The actual charge rates themselves are determined by a combination of the phone and charger. The G4 is QC2.0 compatible. If I'm not mistaken, the OEM charger is not and limits you to standard charge rates. If you have an aftermarket QC2.0 or 3.0 charger, then it'll charge at the faster rates. Those faster rates will not hurt the phone and there's no setting to change it.
About the only workaround would be to leave the screen on. I've noticed LG to be conservative with charging. With the screen off, it'll charge as fast as the charger will let it. With the screen on, it'll throttle the charge rates even if you're not doing anything on it.