This is a good example of the kind of problems that can arise from downloading components from the 3D Warehouse directly into your model, particularly when you don’t purge them if you aren’t going to use them. It is always better to download them into an empty model and then inspect them to see whether they are suitable for your purpose and to clean them up as needed.
Because they are triangulated surfaces, the Voldemort head has almost 60000 edges, and the Oscar statue has a bit over 12000. Though not vast by SketchUp standards, those are far larger than the edge counts in the house, and (as @DaveR noted) having even unused copies of them in the components collection will increase file size. The unused components also have a number of materials associated with them, which too contribute to file size.
Some of these components (again, notably the Voldemort head) are modeled at huge dimensions, so to use them in a model you would in any case want to shrink them down to real size.
Because it was not particularly well built, it will take a fair amount of work to make a solid from the Oscar statue. For starters, it is an assembly of nested groups. Although some 3d Printer slicers will accept a nested structure, SketchUp will not recognize it as a solid. So, you will have to explode the nested groups.
Then you will find that the various pieces have defects such as surface borders (unclosed holes between the exterior and interior) and internal face edges. There are so many that repairing them will be quite tedious. Most of them will need manual action because it is not clear how the surface was meant to be completed as a solid.