JAA are strongly pushing for the ban of all conversions
Would you like to provide a reference for this ridiculous statement?
Also, you will NOT have to "do it all over again". 15hrs is the required minimum training to convert an existing ICAO IR. Many require more, but nowhere near the full course.
Depends on your circumstances. I for example had an IMC rating and quite a number of "sole ref to instruments" hours. ALL those hours count toward an FAA IR. NONE count toward a JAA IR. If you happened to be in a similar position, were in excellent instrument flying currency, it's possible to get through the FAA IR in 10 days, flying perhaps 10 or 15hrs with an FAA CFI. Do it that way and you CAN save a lot of money. Like I said, circumstances....
Also, don't forget that holding any ICAO IR means you are not required to fly the 10hrs instrument training for the JAA CPL. 10hrs training at UK commercial rates is a lot of money.