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Moto phones are quite close to Nexus phones or pure android as commonly referred to
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See Android phone "charging slowly": How to make it faster, for reasons on why charging slowly is displayed, in particular Andrew's excellent answer. To summarise, fast charging/ Turbo charging is achieved by increasing voltage or current or both, i.e. wattage ( being the product of current and voltage), as compared to conventional charging. Andrew's answer explains the values for which such notification appears ( Nexus phone on linked question uses a different type of which charging compared to your device, but that is a minor detail)
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So, the most likely cause IMO, is that your Turbo charger is not working well or it is not receiving adequate voltage ( connect through a voltage stabiliser, avoiding extension boxes). You can verify otherwise by going to service centre and checking with the Turbo charger sample.
Do revert with your findings