IE11 Slow and Hanging

[#1]

IE11 has become almost unusable on my PC over the last 3 weeks. It hangs and freezes temporarily. If I have two or more Tabs open, and close one, the page remains on screen for maybe10-15 seconds before closing.
If I disable or uninstall Adobe Flash Player, speed returns to normal, but I lose functionality.
What is wrong, or what am I doing wrong?

[#2]

You answered your own question - which I suspect is why nobody has responded.  The question is, why does uninstalling Flash Player work?  Perhaps you have some other unintended add-on that uses Flash Player and causes the problems.  Have you tried a full reset of Internet Explorer?   

[#3]

Agree, Adobe flash player is a haven for malware/ spyware and exploits for malicious code.
Unfortunately there are no secure/ reliable alternatives for viewing flash content online in any of the derivatives of the Microsoft Windows OS.
Even Windows 10 ships with Flash for the Edge browser ( a big shot in the foot for MS)
HTML5 is the upcoming standard which will eventually get rid of this rubbish.
YouTube, the BBC (long overdue) and many others are dropping the plugin primarily due this.
Haven't used Flash Player in over 5 years, don't miss it.

[#4]

I enable flash for certain things only then disable it immediately afterwards which speeds up my browser massively, some webpages are just pants though and slow load or freeze and you have to hit the f5 key or the refresh button in the browser