I don't know what the correct value is, however my understanding of IPO's is that a bank buys (underwrites) the shares first and then lists them. This would suggest a large bank has taken a massive financial bet on the company, and I trust they understand the market and SpaceX's current value.

I know this is a lame answer because it's an appeal to authority, but I don't have an opinion on the share price other than very knowledgeable people have agreed it's fair and put up a lot of their own money.

What I do have an opinion on is that I think there's plenty of room for them to expand the market and grow. I also know the EBITDA for SpaceX is outrageously high for a hardware company, would would suggest it's a lucrative industry that others have trouble entering with low recurring costs. It seems likely to me they could continue to grow on 15 billion of revenue, and this growth is likely to be profitable.