The problem is, i'm about done, building a plugin and blueprints for sale on the UE4 marketplace, and haven't had the time to see what would need to be done to get Unreal Build Tool (UBT) to work with eclipse, etc.
So I really cannot help there, BUT Here is what I have done to VS2015 in order to speed it up, since you posted, none of this I came up with, I found it scrounging around through a lot of posts here in the answerhub, and the forum, and I almost must say, that your mileage may vary, as some of the posts/forums, indicated it helped some people, and not others. I'm pretty sure that's all I changed, I played with some turning off some other stuff, but found it had no effect.
If a language service knows possible completions, the Intelli Sense suggestions will pop up as you type.When your waiting, for VS2015 to actually respond, take a look at what its doing, most of the time (not all the time), it will say in the status line, that it's off scanning, or parsing.Eclipse can be fast, and if you load it up with all the plugins available for it, you can slow it down considerably.If you continue typing characters, the list of members (variables, methods, etc.) is filtered to include only members containing your typed characters.Pressing Tip: The suggestions widget supports Camel Case filtering meaning you can type the letters which are upper cased in a method name to limit the suggestions.