What do you intend to do is called HNSC (Host name Site collection) that mean avoid creating multiple web application with multiple application pool,
This is very useful for performance , So there's no issue for performance with this method. for more details check The Expense of Application Pools
But I think the main issue will be related to
capacity planning , where the two site collection will be created in the same content database, so you should limit the number of site collection at the content database
Then create a new one that you hold the second site collection. To lock down a content database check Content Database Consideration
In my humble opinion , In your situation , you have My Site host , so I suggest creating two web applications with the same application pool
- One for the Collaboration Room web application.
- Second for
In this case, you cared about performance, capacity consideration .