In theory, if you have used the same steam account for both versions, it should all transfer across anyway. If it isn't then you could just copy and paste the relevant folders from the TS2014 folder to the TS2015 folder, but ISTR that TS2015 doesn't like this and refuses to let you use it in game. It might be worth contacting dovetail games and explaining what the situation is and what you want to do, but given their previous record of assistance, it might be better to bang your head against a brick will!
"I don't make mistakes. I make prophecies which immediately turn out to be wrong." "And now, excuse me while I interrupt myself" - Murray Walker OBE
Student of Mechanical Engineering at the University of Nottingham (loosed upon the real world for a year)