Try displaying only the paths instead of also the line weights. 

All Adobe products are RAM hogs. You either have not enough RAM to run Illustrator properly or you have too many other programs open. 

That said, Illustrator is the best product at what it does, by a ridiculous margin.

I draw all the paths and geometry in AutoCAD and then import them to Illustrator for coloring and text. That saves lots and lots of heartache.

batman, I would recommend a minimum of 32gb of RAM for Illustrator and InDesign work. Otherwise, this thread has had pretty good suggestions.

Like the above posters, i do as much as possible in cad and go into illustrator at the end for final touches.

I find Adobe's habit of radically rearranging their user interfaces and toolbars in each new release of products maddening.  Bridge was really useful for me until they changed it all up.

Sketch. Mac only right now I think, but it's like photoshop and illustrator combined. People use it for web design a lot as an alternative to adobe CS and it's pretty solid, along with only being 99$ for a lifetime license.