What type of WiFi does the 2015 MacBook Pro use?

802.11ac dual band (2.4GHz AND 5 GHZ with three antennas was introduced in the MacBook Pro line in some late 2013 models (MacBook Pro 11,2 and later) and has been supported ever since then.

Kappy makes a prudent point on available numbers and separate channels.

You can see more about channel separation and overlap:

https://www.electronics-notes.com/articles/connectivity/wifi-ieee-802-11/channels-frequencies-bands-bandwidth.php

From >System Preferences> (option key) System Info>Network>WiFi you can see more on your wireless card.

Holding the option key and clicking the WiFi icon in the upper right menu bar, you see much more on your current situation.

more on 802.11ax

https://www.networkworld.com/article/3309439/mobile-wireless/80211ax-preview-access-points-and-routers-that-support-the-wi-fi-6-protocol-on-tap.html

https://www.networkworld.com/article/3313108/hardware/when-will-we-be-able-to-purchase-802-11ax-access-points-and-client-devices.html

The computer uses standard 10Mbps - 1Gbps Wi-Fi. It will work with any router suitable for home or business use. Read the specs for your model.

The 5 GHz is faster,  does not travel as far,  so less interference with your neighbors and in home devices.

Also, it runs on different and widely separate channels from 2.4GHz.

Nothing wrong with the speed of 802.11n, however the newer 802.11ac speed you mac has the hardware.

IEEE 802.11ax is designed to operate in all band spectrum's between 1 and 7 GHz when they become available in addition to the 2.4 and 5 GHz already existing— and speculated to reach full implementation in 2019

It is the 2.4 GHz that is the most crowded, everybody & everything is on this band

getting a simultaneous dual band router 2.4 and 5 GHz router is probably your best bet.

The 5 GHz is faster, does not travel as far, so less interference with your neighbors and in home devices.