Apple - My MacBook pro Wi-Fi is slow, other devices are OK

Your MCS is zero (0) which would explain why your WiFi is slow.

That can happen if there is channel crowding (not only from your devices but neighbors included).

You could just change the channel for now 1 to 5 and try.

Or you could do a quick analysis of the channels do following:

In Spotlight type "Wireless Diagnostics"

Click on Wireless diagnostics to start it.

Now in the menu bar click on the Window - Utility - WiFi scan -Scan Now.

Sort the result by channel so you can see how crwoded are the channels.

Open your FritzBox set up page and set it to the least occupied channel.

If you do not know how, open any of the following Internet Explorer, Google Chrome, Mozilla Firefox, Safari.

In the address window type 192.168.178.1 , that should open the FritzBox set up page.

The fix provided by Buscar is a good one, but it's only temporary.

Channel crowding is a problem that will only become worse, not better. As more and more people buy wireless routers, range extenders, and additional access points to solve their connection issues, you are going going to run out of channels.

Manually setting your channel today will fix the problem now, but tomorrow when the other wireless routers with their "Auto Channel Setting" suddenly take over the one you have set up, you are back to square one.

There are a couple of things to look at:

• Get a dual band (or even tri-band) router. This will give you many, many, more channels to work with. The upside is that the 2.4GHz frequency will easily go through walls, but it will be very crowded. The 5GHz frequency will be relatively quiet (for now), but has more difficulty going through walls. You said you are only two rooms away...5GHz should be able to get to you with no problem. The downside is that they are pricey. Prices start at $150.
• Run a CAT5e cable. For the price of a high quality router, you can run a CAT5e drop between the two rooms with the cable in the wall. Don't run a 50 or 100 foot patch cable. Put in some plenum rated CAT5e and terminate properly. This will give you a nice, solid gigabit connection.

I personally have done the latter because I had the exact same problem as you are experiencing.

I have a Surface Pro 3 and a iMac that have CAT5e connections on my desk and I have zero connection issues. When I do a scan of my Wi-Fi, I have about 20 different networks all fighting for space (I live in a condo)

Even if you want to "float around" with your MBP and not be tethered to a cable, you can still run the cable and hook up an inexpensive router or WAP, turn down the transmission power of the antennas and ensure a good WiFi network in your room only. (I've done this in the bedroom for the Kindle)

One big benefit is that the gig connection between my computers and my Synology NAS means super fast file transfers. What used to take 10+ mins to copy now only take a few seconds.