Guys! I solved it!
Opera officially loads up in about a quarter of a second now!
Here's the scoop:
I have two EVGA GeForce 1080TI FTW graphics cards, each running three monitors.
I tried disabling one of my cards, and it was blazing fast! I also tried booting in Safe Mode, and again - it was super fast!
I tried all sorts of adjustments... SLI... Display spanning... I even removed my SLI bridge between both cards. All to no avail The minute I enabled all six monitors - there was my 3-second lag again.
I uninstalled the nvidia drivers. This gave me one screen of course, and five blank ones.
I then wanted to try again, so I went to device manager and Scanned for Changes.
All six monitors lit up again... and.......... I clicked on Opera....... and...
The program literally loaded the split second (nanosecond?!) I clicked my mouse. Amazing.
Thank you all so much for all the suggestions! I can't believe it's solved. It seems like other apps are snappier, too.