It's unlikely that anyone would have considered this project had the computer costs been 10 to 100 times higher, as they would have been 15 to years earlier.

Question 1. Is there a reason or a specific situation that one should use inversion in a conditional clause? Does that sentence sound different from "It's unlikely that anyone would have considered this project if the computer costs had been 10 to 100 times higher."? Since I am a foreigner, I can't get the difference..

Question 2. In the following sentence "as they would have been 15 to years earlier.", why can't I use a simple past tense. Like "as they were 15 to years earlier." Does this sentence have different meaning or is it not just not correct in terms of grammar?