This is a great question! You are right about Lightroom not being the fastest way to view your images. It’s powerful, and has an awesome search feature for any field your looking for, but it isn’t necessary fast at loading previews.
If you have Adobe software, I suggest Adobe Bridge. I use that quite often and it loads RAW file previews very quickly.
Before I delve into research on other programs, preferably open source ones, I’d like to hear other’s suggestions and experiences.