Seems too cheap for me, as usual. Unless there are substantial add-ons.
For comparison, James Maddison went from Norwich to Leicester for €25m at age 21. Was he any better for Norwich than James is for Swansea?
Richarlison originally cost Watford €12.4m but was sold a season later to Everton for €39.2m, after proving he could cut it at Prem level. I'm pretty sure Dan will cut it at Prem level - he's a British player, so he doesn't face the same acclimatisation doubts that Richarlison would have, and I honestly don't see any reason James can't match or better Richarlison's impact.
I'd have been happier with £20m (€23m) plus another £5m with x number of league appearances, 10 say. And 20% of the sell-on. And if he's not going to play for the United first team next season, then a season long loan-back.
I understand the club is not in a strong bargaining position. James has one year left on his contract and won't re-sign. That's particularly irritating to me, because I'm sure United would happily match say a £20m minimum release fee. If James's agent was a bit cooler, he would have let James sign a deal with such a clause, his player still gets the big money move, and Swansea get good value back.
All things considered, £15m isn't awful, and I'm happier seeing James go to a big club, both for James's sake and also because it would be insulting for him to leave for Leeds or Southampton or someone similar.