I wouldn't count 150M sold out for the Switch since the Switch pretty much has been blowing expectations ever since launch and it's STILL growing YoY despite the Switch selling insanely well in 2019 alone and it's currently the 2nd fastest selling system after 3 years behind the Wii.
-However, I find it very unlikely it could surpass 150M and I think the main reason why is because the Switch doesn't have the mass market casual appeal like the DS and PS2 did. Where many casuals purchased the DS cause of the touch screen gimmick and also smartphone gaming didn't take off yet, making the DS the only legitimate option to play casual games on the go. And also the PS2 was essentially the cheapest DVD player on the market WHILE being a game console, so many people who weren't even into video games purchased a PS2 just cause it was a cheap DVD player(it also had a ton of games too)
-While the Switch has massively appealed to gamers as the sales prove it, it isn't really appealing to those who aren't that much into video games. Most casual gamers now are ok with playing Candy Crush on their smartphone and they don't see a reason why they should spend 200-300$ on a dedicated game console. While the Switch's hybrid and detachable controllers concept is cool, it isn't really appealing to the soccer moms out there.
-I see the Switch selling around Gameboy numbers between 110-120M and close to the PS4. The only way I could see the Switch getting close to 150M is if they make some type of gimmick or game that appeals well beyond the casual gamers and they extend the life of it by releasing a ton of new models while cutting down the price significantly.