So my experience has been a bit better, but I totally agree with the comments made here. Our projects were in 2015 and things seemed good enough. 2016 came around and I tried upgrading only to find IDE performance and was terrible, with extremely long load times, seemingly unnecessary hour glass, and a Save All that would take about 20 seconds per VI. I reverted to 2015 and told NI about my experience and shared my project. 2017 came out, and it was a bit better so we started migrating projects to it. Upgraded to SP1 as soon as we could. It still wasn't at the 2015 level but I just needed me some VIMs. 2018 came out and I've been thrilled compared to 2016 and 2017. It is hard to say if it is at that 2015 level but in some respects I think it is better. Especially when switching between contexts of different target types. This used to take upwards of 30 minutes to go from a project with one target type, to a project of a different type. Now it is maybe 5 minutes, for this somewhat large project with lots of shared components. I think the main thing NI had to say that was improved, was the checks on if a thing needed to be compiled. In many cases this check to see if things needed to be compiled can be recursive, and waste lots of time when it should be clear to a human that it isn't effected. They tweaked things to make shortcuts in this check that greatly reduced this in some cases like mine.
I'm always surprised to think back and how personally this issue has always been there. Trying to use the latest version of LabVIEW has always felt slow to me compared to the previous couple years. I very vividly remember working in 2011 thinking how terribly slow it was compared to 2009, or 8.6, and how editing code was frustrating. Then a few years later I remember using 2013 and when I would go back to 2011 things felt so much snappier and easier to use. And even further with using 8.0 and 8.20 verses 7.1. It is possible that this is just a sign of computers catching up in performance, and these couple year old versions were made for slower machines.