If I may,
I have played the CA-95; which I believe uses the same action in the MP11SE…
In a nutshell, the P-515 is the winner in terms of overall value despite the ‘negativity’ associated with its ‘folded’ action.
I, too, thought that a folded action would never be as realistic as a ‘long stick’ anchored by a pivot, and coming from owning an MP10 (a while back), which used an action very much like the GF (only slightly shorter), I felt no folded action could match it (RM3) till I bought the P-515!
Now, let’s be clear, we put a lot of emphasis on the action mechanism in isolation, but I genuinely feel that it is the pairing between the action (mechanism) and the sound engine that truly makes all the difference, and Yamaha’s NWX + CFX is truly a match made in heaven. If you ask me, only the N1X surpasses this; however, that instrument costs much more.
Now, to your question, ‘is it worth it, going from P-515 to MP11SE’? No! (in my humble opinion)