Are there limitations in US legislation on a US citizen to own a MiG-15 in Europe?
With mere possession the only issue you might run into is any live, functional weapons on the aircraft. This is governed more by the nature of the device than the person owning it. Generally speaking, Europe is far less accommodating regarding private citizen ownership of military weapons than the US, especially nasty ones like automatic cannons. If they have been demilled to the specifications of the country in which they reside, then they're not guns any more, just decorations. 

A couple of years ago, I saw a Soviet era MI-24 attack helicopter for sale in the US. Main and tail rotors present, no engines, no weapons, cockpit was pretty much gutted, airframe was past its useful life, for static display only. It looked intact from the outside... and also looked very sinister. For some odd reason, my wife balked at me spending $8k on this ultimate lawn decoration. But, there were no regulations regarding its ownership, other than maybe a neighborhood association getting huffy about someone parking an attack helicopter in their front yard.  

Now, if you want to actually fly the MIG15, that's a different matter. But if you as a US citizen want to purchase a MIG15 as a static display, without functional weapons, the only thing the US government is going to care about is whether you paid their income tax on the money you use to buy it.