This site says that I should be using the gravestone doji in timeframes that are 1 hour or up is this true can it not have meaning in the 15 minute timeframes?
Well, trade the 1h and up then.
Every thing on charts has less meaning the lower the time-frame you use, and that isn’t unique to gravestone dojis. It also applies to support and resistance, chart patterns like head-and-shoulders, other candlestick patterns, trend-lines etc. Almost all of these were originally identified and evaluated from daily charts, so technically use on a lower time-frame is already misuse.