Somehow the questions seem familiar to me... Both are suitable for portraits, for example.
In my opinion, the surcharge is definitely worth it.
The Sony has a 1.8 aperture - the Sigma only a 2.8.
In addition, the Sony has an image stabiliser - the Sigma does not.
Even if it costs twice as much - I don't think the joy of using the Sigma will last very long. Better to buy the right one than 2x, it's even more expensive.
I don't have to say anything more about the 1.5 crop factor...