I’ve imported DWG files much larger than 15mb. Usually if you wait long enough it will import. An overnight wait does sound excessive however. The spec of your PC is a potential issue, although short of spending more money is not easy to address.
An easier fix however is to break down the source file. In your CAD software you could look at stripping out unnecessary geometry and layers. If you need all of the information however then you could break down the geometry into separate files (either physically cut it up into tiles or split it into different layers per file) and then import them one file at a time. If you check ‘preserve drawing origin’ on the options before you import it will bring in the geometry in the correct locations and assemble it one file at a time.