Yes, of course. I think there are at least 2 things you could do to reduce the time to charge our iPhone.
First, charge it through the charger that comes along with your iPhone rather than via a USB port on a computer. The charger simply provides more amperage than the USB port. Or, if you really have to charge via the USB port, plug your iPhone to a USB 3.0 port: the current limit of a USB 3.0 port is much higher than that of a USB 2.0 port (still no way to beat the iPhone charger though.)
Second, don’t use your iPhone while it is still charging. For one, and this is quite obvious, if you use your iPhone when it is plugged into a charger, then some of the power it receives from the charger must be compensated for running the applications that you are using. For another, it is probably much less known that heat is really a big factor in the charging process. If the battery is in high temperature, then not only will its capacity and life span be compromised, but it will also take longer to be completely charged. This is just one of the inconvenient facts about Li-ion batteries. I recommend you to always plug in your iPhone to a charger before you go to bed, so it wouldn’t be much trouble if you switch it to airplane mode or shut it down completely.
Hope I have answered your question of why is my iPhone taking so long to charge.