Unfortunately there doesn't seem to be a way. As far as I know it charges to around 4-5% of battery capacity so that it's sure to be able to perform the whole boot process, even if it's unplugged, so not to screw something up when losing power while starting up the OS. 15-18 minutes seems long to me, though. It's usually 5-7 minutes using the iPhone charger. Are you charging off a PC USB port?

I solved this choppy audio issue with just one simple trick. (This might not work for everyone, but I solved it this way)

Short answer

If your hardware uses Bluetooth 4.0 instead of 4.2 or above, this solution is highly likely to work for you.

Open System Preferences > Sound > Input

Change sound input from Airpods to Internal Microphone

Long answer (+ Possible explanation)

(This is just my hypothesis based on my observation)

First of all, to clarify my symptoms, I am using a MacBook Pro 15 inch (Late 2013) which has Bluetooth 4.0 hardware. The choppy audio issue only happened in my MacBook Pro, and it did not happen in my other Apple devices such as my iPhone 7 Plus (which btw, has Bluetooth 4.2), nor my iPad Pro (also Bluetooth 4.2).

Based on these observations, my hypothesis is that Bluetooth 4.0 devices have too low bandwidth to handle both input/output (microphone & speaker) at a high quality. However, if I just change the audio input to the internal microphone, the Bluetooth connection only delivers sound output, so I think it can handle higher quality audio. On the other hand, if I use both microphone & speaker on a Bluetooth 4.0 device, I think the connection degrades and sacrifices audio output bandwidth in order to make room for delivering audio input.

Indeed, according to some sources, Bluetooth 4.2 is 250% faster and has 10x more capacity

Reference:

1. https://www.quora.com/What-are-the-main-differences-between-Bluetooth-4-0-4-1-and-4-2-in-the-Layers-Baseband-LMP-L2CAP-app-Layer
2. https://www.semiconductorstore.com/blog/2015/BLE-4-2-vs-BLE-4-1/1548/