Macbook bad internet connection WIFI I rented a room in a shared house (we are in 5).

What I've noticed is from my room the internet connection is really bad (sometimes it doesn't even load the google homepage).
My guess is not that the bandwith is saturated even though there are 5 of us, instead that there is some kind of router problem in managing many devices all at once (like if I turn off my cell wifi gets slightly better).

Today I was downloading a file at 1.5 mb/s from this connection even though pages struggled to load, but as soon as I clicked the download button it went straight up to 1.5 mb/s with a decent speed stability.

Moreover I think the signal is good enough 4/4 in the indicator at the top-right of the screen.

How can I solve this? I also noticed my cell has kind of priority if compared to my mac since sometimes when I cannot even load google with the pc I can navigate with my cell browser.

What is the reason behind this? Are there any solutions? If there's this "priority system" how can I put my pc at the top?
Over time, Wifi hardware has progressed through several versions. In addition to higher speeds, the newer versions tend to offer better connection quality when there are many wifi signals and other interference in the vicinity. It could be that your computer has older wifi hardware than your phone, and hence is not able to handle the interference as well, producing slower speeds.  Interference is especially likely if you live near many other homes with people using wifi, too. 

If you are on a Mac (assuming you are because this is AskDifferent), you can see what Wifi revision your Mac supports by doing the following:
Click the menubar Apple logo in the upper left corner of the screen, then "About this Mac", then "System Report", then "Wi-Fi" mid-way down the list on the left.  About 14 lines down in the right-hand pane, you should see an entry for "Supported PHY Modes:".  Next to this you'll see something like "802.11 a/b/g/n/ac". Those letters indicate the WiFi versions your hardware supports, with "a" being the oldest, and "ac" being the newest. Versions "n" and "ac" in particular added improved support for handling lots of interference from congested airwaves.

[Added based on receiving more model information from OP:]
You have support for wireless version "n" in your laptop, but not version "ac".  There may be a performance difference between these two standards in your situation.  If you can find a machine (computer, cell phone, tablet) with support for "ac", try testing that in your room to see if speeds are better than you are getting on your 2008 Macbook. If so, then this is the issue (and please up vote this answer; thanks!).