From what I've been told (but not experienced myself), JRiver MC has been tested with collections of over 1,000,000 tracks. 150,000 titles at an average of 10 tracks per title works out to 1.5 million. I'm not sure how a collection of that size will perform. I would expect performance to be fine, but I'm having trouble locating examples of collections that large in forum postings.
But let's step back for moment. You've got a massive cataloging project to conduct. I would expect that you, or someone you hire, or even a small team (2 or 3 people) are going to be busy with this for quite some time. Making sure that this is approached in a very structured manner is going to be important.
With a collection this size, figuring out the exact release of each disc (or other recording media) you have becomes much more important than in a more modest collection. You're bound to have a good bit of overlap including true duplicates, different release numbers which are actually also duplicates, and of course re-releases that are unique from the original.
You've probably thought through all of this and more; it's just something that's been on my mind recently, so I wanted to share a few of my thoughts.
If I were doing this, I would start with the physical collection and get it as organized as is practical, trying to group artists and albums together as a start, so you can have an overview of the collection you plan to digitize.
Finally, I'm certain everyone has said this, but make sure to have a robust backup strategy in place from day one. This should include backups going to a separate offsite physical facility periodically in case of fire, theft, or other disasters at the primary site.
Sounds like it might be fun actually.
Good luck.
Brian.