How long does conversion from mesh to solid body usually take?

I have Fusion360 on my laptop(not much processing power) and am trying to convert a sheet body (STL of a character bust) to a solid model so that I can perform boolean operations such as using a subtract tool to make a hollow mould of the figure. I have closed all the holes and reduced the number of facets, but still get a warning that the total number of facets exceeds 10,000, and the program just seems to freeze and not do anything when I click ok to perform the operation. Is this simply an issue of processing power of the laptop or does conversion of sheet bodies with a high amount of facets always take a longg time?