4-hour I could possibly understand for the reasons given. Not 15-minute though.
Post charts maybe and I can compare for you on two or three other live accounts with different platforms and data feeds???
Are they ALL different or just one instance of a particular 15-minute bar???
Of the two though: I’d go with Forex.com if those were your only two options. Forex.com belongs to Gain Capital and who used to be the FOREX provider for TradeStation Securities.
Not that they SHOULD differ though. But that’s retail spot FOREX for you.