Unless I'm being lied too, and there is no reason why this would be as it comes from someone inside Liverpool, the release clause is definitely £15m.
HOWEVER
For what reason I don't know but LFC seem to think they can get him for less and £12.5-13.5m has been mentioned but not certain. Same person told me Swansea are happier to negotiate a sale than they are making out in public and have conceded they will lose him.
I don't know where this supposed interest from Spurs is coming from because nobody in the know their end has heard anything about it and have told me they wouldn't go anywhere neat £13.5m for him, let alone, £15m and AVB is adamant he wants Moutinho. They also told me Spurs spending is finished until they sell some players to generate funds as they have spent their free cash on Vertonghen and Sigurdsson and have agreed a price and wages for Adebayor so need to sell Modric now which could drag on yet.