Startup lag when playing audio on Bose NC 700

I recently got a Bose NC 700 bluetooth headset to use with my desktop machine, and I've been experiencing a strange issue: after a specific period of silence (seems to be pretty close to 15 seconds exactly) there's a very slight delay (maybe 0.5s) before audio starts playing again.

It's not a synchronization issue; the beginning of the audio simply gets cut off, but the rest is played properly. Long periods of audio output work fine, and stopping and re-starting audio also works fine as long as the silence is shorter than 15 seconds. However, it makes certain use-cases pretty painful, such as the inherently intermittent audio from some flash-card apps I use.

I've noticed that the silence after playing audio is also accompanied by a very slight, barely discernible high-pitched hiss that cuts off entirely after the 15 seconds, but this seems to happen with other bluetooth headphones as well (which don't have this startup lag issue), and also occurs when playing audio from other devices (e.g. my phone, which doesn't have the startup lag issue), so I'm not sure if it's just a bluetooth quirk.

My initial guess was that it was some kind of bluetooth or USB power management issue, but my attempts at disabling it haven't worked.

• Tried blacklisting the bluetooth dongle via tlp, based on this answer: https://askubuntu.com/a/370406
• Tried disabling btusb.enable_autosuspend via a config in /etc/modprobe.d/, based on this post: https://ljn917.wordpress.com/2018/03/01/disable-bluetooth-autosuspend/

Some more specs:

• Bluetooth dongle: https://smile.amazon.com/gp/product/B009ZIILLI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
• Pulseaudio version: 11.1
• bluez version: 5.48
• kernel: 4.15.0-108-generic