Maybe the chargers that you've used before were slower than the 1.2A charger that ships with Nexus 5?
It makes sense now if your using the Nexus 5 stock 1.2A charger, that to charge 80% of a 2300mA battery (i.e. 1840mA needed to be charged) it would take somewhere around 2 hours or less. 1840mA divided by 1200mA equals 1.5 hours. I don't see though that this would require special rapid charging from the phone's chip -- just typical charging rate with a 1.2A charger?
And according to Brian Klug at Anand Tech, the Qualcomm Fast Charging mode is not being used by Nexus 5. In Klug's review, he found that using the supplied 1.2A charger, the Nexus 5 is charging at a rate of about 1000mA, which results in full charge (0 to 100%) in about 2.5 hours.
Here's the quote from the review (
AnandTech | Google Nexus 5 Review ):
When it comes to charging, Google continues to do the sane thing and implement BC 1.2 signaling. Unlike the LG Optimus G, the Nexus 5 does not use the battery charging IC Qualcomm makes for use in conjunction with its normal PMICs, instead it uses the TI BQ24192 to charge at up to 1.5 A maximum and a MAX17048 fuel gauge. This seems to be done in order to accommodate wireless charging, though there could be other cost considerations at play. The Nexus 5 seems to charge in the linear region at just above 1 A however, although the limit set for BQ24192 is 1.5 A, and has a total charge time just above 2.5 hours on the supplied 1.2 A charger.