£15m seems to be not a lot to get a complex jet aircraft from "mothballed" to air worthy.
The Wikipedia (so taken with a large pinch of salt) page on the return of one of the stored Tu-144's to flight for the NASA tests in the 90's claims (without a citation) that $350m was spent. Now that would have included work to kit out the aircraft as a flying lab, and may, or may not have included the costs associated with fitting the airframe with different engines.
Either way, the work would have been done with the support of Tupolev, I'm not sure Airbus would be wading in with any large amounts of help.
JAS