I went through something similar years ago and learned that waiting indefinitely only makes things worse. What worked for me was sending him a clear message (better in writing so you have proof): "We need to have a serious talk about the 150k I lent you. It's not about our friendship, it's that I really need that money back. When can you return it?" No reproaches, no drama, just straight to the point. Most people who avoid the topic do it because they feel embarrassed or think that if they ignore it, it'll magically disappear.
After that, agree on a concrete date - not "soon," but "September 15th" or whatever's realistic. If he doesn't follow through by that date, then you've got to make a decision: do you push back one or two more times, or do you write it off as a loss? Some friendships are worth losing if the person won't respect your boundaries or your money. It's rough, but friends who lend-shame you like that almost always do it to others too. If you end up losing the friendship over asking him to return what's yours, the relationship was already broken.