I'm not an expert when it comes to how Orion IOS allocates and offloads memory. But like all transistor based computers, there is a fundamental limit to how much data can in stored in memory, therefore when you approach that limit other processes can take longer and performance is reduced.
150 tabs is excessive and if you didn't see a performance decrease I'd assume it's some form of witchcraft.
An iPhone 12 Mini has 4GB of ram, having 150 tabs open at all is impressive.