My mac mini is sitting next to my mac book and the mac mini is crawling while on wi-fi. Macbook is fine. Turned off bluetooth as suggested by some and it seemed to kick back good for about 10 min then back to dial up speed. What to do?

Do you have any USB 3 devices connected?

Is there anything shielding the Mini, like is it in a cubbyhole?

When slow, press and hold the Option key and then click on the wifi icon in the menu bar. Post a screen shot of the windows that opens.

Start up in Recovery mode. In the OS X Utilities screen, select Get Help Online. A clean copy of Safari will launch. No plugins, such as Flash, will be available. While in Recovery, you'll have no access to your saved bookmarks or passwords, so make a note of those before you begin, if they're needed for the test.

Test. After testing, restart as usual and post the results.

What is it with USB3 items that stop WiFi? I bought a USB3 Hub and my WiFi quit. I just unplugged it and the Wifi stated again??? Plugged it back in and it is still working. Will I have to unplug it every time I reboot??? (Mac Mini Late 2014) OSX 10.11.3)

It the frequency associated with USB 3 that is the problem. The frequency is in the range of wifi frequencies. especially wifi networks that use the 2.4 GHz band