Robert wanted to sign him a year ago but he turned us down because he wouldn't have gotten the game time. that all changed once Neymar left this summer as you can see.
It's easy to say that he cost 15 mill a year ago but you must take into account the will of the player . He knew he would be a bench player with Neymar here a year ago.
There is something seriously strange with that 15m fee a year ago. He was a phenomenon in France at 18 years old, dominating the league. That is not something that should only cost 15m a year ago.