Bluetooth Audio interfering with WiFi?

My Wi-Fi is slow or completely broken when using Bluetooth headphones. It is said that this is a well know issue, as Bluetooth and Wi-Fi share the 2.4GHz frequency.

Is this something that could be solved? Are cheap/low-end devices more problematic than quality ones?

What I Have Tried

1. Disable coexistence in iwlwifi, as suggested by Pilot6, by running the following command and rebooting:

   sudo tee /etc/modprobe.d/iwlwifi-opt.conf <<< "options iwlwifi bt_coex_active=N"
   

   This was only a slight improvement, as it changed the speed of Wi-Fi from zero to unusably slow.

2. Try different channels on router.

   I tried both ends of the spectrum (1 and 11), neither created any improvement. Wi-Fi still broken as soon as headphones are turned on. Setting router channel to auto has the best results so far.

System Info

$ uname -a
Linux alien-box 4.15.0-29-lowlatency #31-Ubuntu SMP PREEMPT Tue Jul 17 17:49:04 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

$ lspci -knn | grep Net -A3; lsusb
04:00.0 Network controller [0280]: Intel Corporation Wireless 7265 [8086:095a] (rev 59)
    Subsystem: Intel Corporation Dual Band Wireless-AC 7265 [8086:5410]
    Kernel driver in use: iwlwifi
    Kernel modules: iwlwifi
Bus 002 Device 002: ID 8087:8000 Intel Corp. 
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 8087:8008 Intel Corp. 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 006: ID 1058:07a8 Western Digital Technologies, Inc. My Passport (WDBBEP), My Passport for Mac (WDBLUZ)
Bus 004 Device 005: ID 0bc2:ab31 Seagate RSS LLC Backup Plus Desktop Drive (5TB)
Bus 004 Device 004: ID 2109:0812 VIA Labs, Inc. VL812 Hub
Bus 004 Device 003: ID 2109:0812 VIA Labs, Inc. VL812 Hub
Bus 004 Device 002: ID 2109:0812 VIA Labs, Inc. VL812 Hub
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 005: ID 08bb:2902 Texas Instruments PCM2902 Audio Codec
Bus 003 Device 004: ID 28de:1142  
Bus 003 Device 003: ID 8087:0a2a Intel Corp. 
Bus 003 Device 002: ID 062a:4101 Creative Labs Wireless Keyboard/Mouse
Bus 003 Device 010: ID 2109:2812 VIA Labs, Inc. VL812 Hub
Bus 003 Device 009: ID 2109:2812 VIA Labs, Inc. VL812 Hub
Bus 003 Device 008: ID 05e3:0727 Genesys Logic, Inc. microSD Reader/Writer
Bus 003 Device 007: ID 0b33:0020 Contour Design, Inc. ShuttleXpress
Bus 003 Device 006: ID 2109:2812 VIA Labs, Inc. VL812 Hub
Bus 003 Device 011: ID 0d8c:0012 C-Media Electronics, Inc. 
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

$ lsmod |grep 'bt\|blue\|rfcomm\|bn'
rfcomm                 77824  4
bnep                   20480  2
btusb                  45056  0
btrtl                  16384  1 btusb
btbcm                  16384  1 btusb
btintel                16384  1 btusb
bluetooth             548864  33 btrtl,btintel,bnep,btbcm,rfcomm,btusb
ecdh_generic           24576  2 bluetooth