There is no definitive answer to this question as it depends on a number of factors, including the type of terrain you ride, your riding style and your personal preferences. That said, 150mm of travel is generally considered to be on the upper end of the spectrum for mountain bike suspension and may be too much for some riders.
If you're someone who likes to keep their bike light and nimble, or if you mostly stick to smooth trails, 150mm of travel could be overkill. On the other hand, if you're a aggressive rider who tackles tough terrain often, 150mm could be just right. Ultimately it's up to you to decide whether or not 150mm is too much travel for your needs.