Could I demand for even more than 1.5 at the project's company -> Yes absolutely. First, decide if you want to move for double the salary. Then ask for 2x. If t

Could I demand for even more than 1.5 at the project's company -> Yes absolutely. First, decide if you want to move for double the salary. Then ask for 2x. If they say yes (they likely would), tell your employer: I love it here, but they're doubling my salary, I have to take it.