I don't know if Lotus will develop a car like that; by now Lotus is slower than Toro Rosso in the same PU, starting with a new PU means a new car design and adapt to this PU to compete with the other Merc Powered teams, at best i see Lotus in 2015 as McLaren is now, not considering McLaren have better engineers and way more budget while Lotus lost a lot of important staff last year and i don't see either of their drivers as pilots who can help develop a good car, and that just with the other Mercedes powered teams because its not like Ferrari will be in 2015 as it is now, RedBull will improve a lot now that Renault will fully focus on them, Mercedes will never give a full support to a customer team because they are focus on their factory team so my safe bet would be Lotus constantly fighting for points and an eventual podium but i don't see them at the front of the grid.
I imagine Toro Rosso got a whole lot of help from their daddy in integration and running of the powerplant.
Lotus seem to be struggling with this quite badly still. Look at Sauber as well - having a load of trouble with the Ferrari powerplant.
I think that the Mercedes is just way ahead of the game and will be much easier to plug in and get to racing.