A Google search on "D4NN6015F" seems to indicate that it's a smaller displacement engine than the 201 that your 545 originally had. Most hits seem to claim that it's for a 3000, 36000 and/or 2600, which would make it a 175 ci engine, but I found one post from Tony Jacobs where he says that it is a 192, which would make it from a later tractor, like a 3610 or 3910, which would have a bit more hp than the 175, but not quite as much as the original 201 had.
Anyway, that's plenty enough engine to run your loader and do whatever else you plan to do with it. The loader runs off of hydraulics and has a pressure relief vale that's going to open up long before the engine runs out of power, and the wheels will lose traction long before it runs out of power as well.
Here's a link to Tony Jacob's statement that it's a 192:http://forums.yesterdaystractors.com/ttforum/viewtopic.php?p=4856115&sid=0d1a0099d246f3013b4731eed837667b